METHOD AND APPARATUS FOR CONTROLLING THE GAS CONTENT OF DISPENSED HOT MELT THERMOPLASTIC ADHESIVE FOAM

摘要

METHOD AND APPARATUS FOR CONTROLLINGTHE GAS CONTENT OF DISPENSED HOTMELT THERMOPLASTIC ADHESIVE FOAMAbstract of the DisclosureA method and apparatus for controlling thegas content of dispensed hot melt thermoplasticadhesive foam. Air or another relatively inert gas ismixed with molten thermoplastic adhesive, and themixture is pressurized to form a gas and moltenadhesive "solution". When the molten adhesive and gas"solution" is dispensed at atmospheric pressure, thegas is released from "solution" and becomes entrappedin the adhesive in order to form a homogeneous closedcellular adhesive foam. In order to control the gascontent of the dispensed adhesive and gas "solution"in accordance with one preferred embodiment, thepressure drop across a restriction in the flow path ofthe solution is sensed, and a control circuit controlsthe addition of gas to the adhesive to maintain thesensed pressure drop at a desired level. Othersensing techniques can be used to measure a parameterof the dissolved gas/molten adhesive single phaseliquid solution which is correlated to the dissolvedgas content of the solution and substantially indepen-dent of the molten adhesive content thereof, such asmeasuring the transmittance of infrared radiationthrough the gas/adhesive single phase solution at awavelength relatively heavily absorbed by the gas andunabsorbed by the adhesive.