Hot melt adhesive
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- Glue gun redirects here; for the band Glue Gun, see Glue Gun (band).
Hot melt adhesive (or hot glue) is a form of thermoplastic adhesive that is commonly supplied in solid sticks designed to be melted in a special gun. The glue comes in cylinders of various lengths, and is pushed into an electric hot glue gun. The gun contains a heating element to melt the plastic glue, which operates all the time the gun is plugged in. Squeezing the trigger pushes the stick through the heating element, ejecting molten glue which is initially hot enough to burn and blister skin. The glue is tacky when hot, but hardens and stops being sticky in a few seconds—a minute at most.
Animal glue which is applied hot has been used in woodworking since the time of the Ancient Egyptians. It is heated in a glue pot and applied with a brush.
However, the most common application for hot melt glue is industrial. Hot melt can be found in many products that we purchase each day.
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[edit] Glue sticks
Glue sticks are manufactured in several diameters for different glue guns. The most-used size has a diameter of 11 millimeter (about 0.45 inches). Sticks are available in various lengths, from about 10 centimeters up, although guns will take sticks of any length. Thinner 7 mm 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.
For domestic use just a few types of stick are available, and more or less interchangeable. For industrial use many types of sticks are available for special purposes, with diameters of 12, 15, and 45mm in diameter. 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.[2]
[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 250º F (120º C), and are well suited when high temperatures are undesirable, for lace, cloth, children's crafts, etc. High-temperature guns heat up to around 380º f (195º 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, or lack of brittleness, 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.
[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
- Arrow heads may be held on with hot glue, allowing removal (e.g. recovery of head from a broken shaft) with the heat from a small flame.
