" " wisno wood furniture finishing: Hot melt adhesives

Monday, July 16, 2012

Hot melt adhesives

Hot melt adhesive is one of  the types of glue that is most used in the woodworking industry. This glue has a solid form at room temperature, and it need to be heating in its application. In the hot condition it will melt and form a liquid, then he can be coated at the surface.  Two faces application is needed and then after the 2 pieces be unified then he will cool and harden to form a strong bond. Hot-melt adhesive is mainly used in specialty applications, mainly due to its ability to form bonds quickly. It is most used in the furniture and cabinetry assembly, window construction and edge banding of panel or decorative laminates. Rapid bond formation is the advantage of this glue. It is preferred in the manufacturing operations because of the minimal clamping time is needed. The hot melt adhesive is very practical and easy to use with the strong and thermosetting adhesion result. No thinner or solvent that will thin the glue and reduce the strength of the glue mixture. Neither the water that will affect the moisture contents the interface. The disadvantage of this glue is its high price and the fact that the glue in some condition cannot perfectly wet the surface as well as the glue that use solvents.
There are several types of hot melt adhesive but according to its formulation it can be grouped to the ethylene vinyl acetate and polyamide. This ethylene vinyl acetate is made by gas-phase polymerization to yield non-solvated polymers. It has wide range of properties according to the ratio of vinyl acetate polymer and molecular weight of the polymer. It is relatively inexpensive, but some time it has problems with creep as the temperature increases. Since they contain large amounts of lower molecular weight in the adhesive formulations and there is limited attraction between the polymer chains. It is used more paper products than with wood products.
Polyamide hot-melt adhesives have stronger bond with better creep resistance. It has the strong hydrogen bonds between the chains make it has better creep and heat resistance. It is quite expensive make it is more used to the high-value products that need more durable bonds. It most used in the furniture assembly, windows or door construction and edge banding.
Hot melt adhesives need the heating machine in the application process. The tool mainly is container, which is equipped with a heater to place the glue, hose and a gun to apply the hot glue to the desired surface. The temperature needed could be vary depend on the type of glue used, but usually the glue will start melting at temperatures around 80 C, but usually he need to be heated at temperatures about 150 to 200 Celsius to achieve low viscosity in the application. And since the glue will hard and set when it is cold, the machine need to keep hot when it is contained the glue. The glue should be release from the machine and the equipment should be cleaned when it is stopped operating. The cleaning is done by set the temperature at the point where the glue starts to melt (about 80 – 100 Celsius) and drain the glue out, then flow glue thinner to clean the lines and hose. Make sure there is no glue left in the machine, line and the gun before leave the machine, since the rest of glue in the machine will be harden and clog the line.

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