Hot Melt News

Polyurethane Reactive Hot Melt (PUR) has become an important fastener for manufacturers. It is used in thousands of assembly applications worldwide from woodworking to aerospace.

PUR Hot Melts are such a valuable product because they are an easily processed single component adhesive that bonds very quickly to a wide range of substrates then cross links to form an extremely strong flexible bond that is not easily reactivated. PUR’s offer good strength and flexibility at high and low temperatures with a wide range of substrates to include plastics, metals, glass and wood.

PUR Hot Melt cures with moisture found in the air and the substrates. It is for this reason that PUR must be kept in air tight desiccated containers. The containers PUR’s are available in are 310 ml aluminum cartridge, 2 Kilo slug sealed in a foil bag, 5 Gallon/20 Liter pail and 55 Gallon/ 200 liter drum.

Cartridge guns are used to process PUR in cartridge form. The front of the cartridge is pierced and the nozzle adapter attached. The cartridge is inserted in the gun and heated. Cartridge guns can dot glue, extrude beads, swirl and spray. The maximum melt rate for these guns is 2 cartridges per hour and the use of a cartridge pre-heater can accelerate the melt rate. Actual output rate using these tools can exceed 1 cartridge per minute depending on the adhesive viscosity.

For “Hands Free” assembly cartridges are also being manually opened, the adhesive removed and cut in half and inserted into nitrogen pressurized melt tanks for extrusion. Specially designed heated pressure vessels are pressurized with nitrogen to keep moisture away for the PUR and to create adhesive flow through check valve nozzle tips. PUR in 2 Kilo slugs is also being pared down in size and processed in the heated nitrogen pressure vessel extruders.

Standard hot melt systems with small reservoirs and customized lids are also being used to process PUR. Very low flow regulators are used to nitrogen blanket the PUR in the reservoir keeping any moisture from the adhesive. Regular system purges are important to insure long term performance

Another system used to process PUR in slug for is a customized reservoir with dry air purge feature. After inserting the 2 Kilo slug these systems desiccated the air in the reservoir is replace with desiccated air and held at negative pressure.

The most cost effective way to process PUR, if your usage allows, is in pails or drums with pail or drum unloaders. These systems force a heated platen into the container, effectively purging all air between the adhesive and platen and the adhesive. Used properly pail and drum unloaders seal the pail or drum without the need for dry air or nitrogen blanketing.

Polyurethane Reactive Hot melt should be considered for the fast, permanent bonding of substrates. This adhesive can eliminate the need to clamp or hold a product in compression and delay production.

For information about PUR systems and adhesives please call Pierce Covert, President of Glue Machinery Corporation at 1(888)202-2468 or email Pierce at info@gluemachinery.com

Hot Melt Stick glue guns are very important to industry for assembly and packaging. These hot melt application tools allow manufacturers to manually apply hot melt adhesives from lightweight, low cost applicators using easily handled sticks of glue. These guns can be purchased at your local craft stores, home centers, on-line or from industrial suppliers of the guns and adhesives.

Hot Melt Stick glue guns offer very different performance characteristics and should be evaluated closely to fit the application. The key difference between hot melt stick guns are their melt rate capacity. As we all know from experience, simply depressing the trigger on a hot melt stick gun does not always insure consistent hot melt beads are extruded from the nozzle.

Hot Melt Stick glue guns quickly and efficiently melt adhesive in the tip where a high temperature heated cone is located. High temperature and the downward pressure of the adhesive stick against this heated cone creates the flow required from the nozzle. Too much trigger pressure relative to the melt rate capabilities can force adhesive past the stick and back into the stick chamber. This usually results in a very sluggish gun trigger, leakage from the nozzle and in many cases ruined hot melt stick glue gun.

Also, the stick or slug adhesive used must be the correct size and offer exact expansion coefficient relative to the gun. The hot melt in stick form actually expands before melting and forms a seal that keeps the hot melt from migrating back into the stick feed chamber.

Typical hot melts available in stick form are limited to EVA’s ( standard hot melts), polyamides ( high temperature hot melts) and some APAO ( polyolefins). Most of these products have limited “Open Times” or working time and require fast lamination of the two substrates.

While Hot Melt Stick glue guns will always have their place in the manufacturing and packaging processes new economical alternative bulk hot melt guns and bench-mounted bulk systems are available to melt and apply a much wider range of low cost hot melts at much faster rates. Hot melt bulk glue guns with reservoirs in the applicator offer good melt rate and high output rates of these adhesives. Where possible, bench mounted systems are being used to apply adhesive to substrate with the actuation of a foot switch so that the operator does not need to handle a hot melt stick glue gun.

For hot melt stick glue gun and adhesive recommendations as well as bulk gun and bench-mount system recommendations: please call Pierce Covert, President of Glue Machinery Corporation at 1(888)202-2468.
or email info@gluemachinery.com