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Jiangsu Kuntai Machinery Co.,Ltd

Hot Melt Adhesive Features

About Hot melt adhesive and PU Reactive Hot melt adhesive 

Hot melt adhesive (HMA), 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 mechanical 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 solidifies in a few seconds to one minute. Hot melt adhesives can also be applied by dipping or spraying. This was invented by Miles Kent in 1894.

In industrial use, hot melt adhesives provide several advantages over solvent-based adhesives. Volatile organic compounds are reduced or eliminated, and the drying or curing step is eliminated. Hot melt adhesives have long shelf life and usually can be disposed of without special precautions. Some of the disadvantages involve thermal load of the substrate, limiting use to substrates not sensitive to higher temperatures, and loss of bond strength at higher temperatures, up to complete melting of the adhesive. This can be reduced by using a reactive adhesive that after solidifying undergoes further curing e.g., by moisture (e.g., reactive urethanes and silicones), or is cured by ultraviolet radiation. Some HMAs may not be resistant to chemical attacks and weathering. HMAs do not lose thickness during solidifying; solvent-based adhesives may lose up to 50-70% of layer thickness during drying. 

There are a number of hot melt adhesives in use, with the most common being those used for hot melt pressure sensitive adhesive applications:

•ethylene vinyl acetate (EVA) copolymers, compatible with paraffin, the original hot melt;

•styrene-isoprene-styrene (SIS) copolymers;

•styrene-butadiene-styrene (SBS) copolymers;

•ethylene ethyl acrylate copolymers (EEA);•polyurethane reactive (PUR).

The latest hot melt adhesive advance is the PUR adhesive, which is a 100 percent solid, one-component urethane prepolymer that "behaves like a standard hot melt until it reacts with moisture to crosslink or chain extend, forming a new polyurethane polymer." By curing the polymer in this way, PURs have performance characteristics that are more enhanced than those of standard hot melts. Unlike many of the other hot melts, which require a slot die or roll coater, PURs are applied to a substrate as a dot or a thin glue line, set in seconds, and are structurally rigid in minutes, following a final set.

Polyurethane Reactive hotmelts are produced by converting a mixture of different (polyester-) polyols with a surplus of a polyisocyanate component. This results in isocyanate-terminated prepolymers with an NCO-content of typically 2 to 5%.

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