Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1984-01-11
1985-10-29
Dawson, Robert A.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
156291, 264 51, 425376R, 4283175, B32B 3130
Patent
active
045499152
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with foaming thermoplastic compositions e.g. hot melt adhesives.
TECHNICAL FIELD
Hot melt adhesives are known and used in a variety of industries. They find use particularly in repetitive production line operations where their capability for rapid application and fast set up are advantageous.
BACKGROUND ART
It is known that the ability of hot melt adhesives to be spread in their molten form is encumbered by rapid set up of the adhesive in the bond. It has been proposed to improve the spreading ability of a hot melt adhesive by forming a foam of the hot melt adhesive, applying it between substrates and pressing them together whilst the foam is still hot. U.S. Pat. No. 3,362,036 discloses extrusion of a mixture of hot melt adhesive and air or other inert gas by means of an extruder in which the adhesive is melted. UK Patent Specification No. 1562562 discloses forming a foam of hot melt adhesive and gas, pressurising the foam to force the gas into solution and then dispensing the adhesive solution. German Offenlegungsschrift No. 2935580 discloses the use of a blowing agent decomposable by heat to bring about foaming of a hot melt adhesive.
Proposals for providing hot melt adhesives in foam form have generally required use of equipment significantly different from that normally used for application of hot melt adhesives, or the formulation of adhesives with selected blowing agents.
Among objects of the present invention are to provide a method and means for providing a foamed mass of thermoplastic composition on a substrate using available compositions, especially hot melt adhesives, in conjunction with commercially available applying equipment appropriately modified by comparatively simple changes.
DISCLOSURE OF THE INVENTION
We have now found that hot melt adhesives and sealants can be foamed by use of moisture to provide compositions of good spreadability, and setting speed. We have also found that a commercial applicator may be used in this process which is provided with an applicator nozzle and which is modified by addition of means for supplying water entrained in a stream of carrier gas to the location at which the hot melt is dispensed from the nozzle.
The invention provides in one of its aspects a method of providing a foamed mass for use in an adhesive bonding or sealing process in which a thermoplastic composition is melted by heating to a temperature in excess of 100.degree. C. and expelled from an applicator in admixture with a foaming agent characterised in that the foaming agent is provided by feeding water to the melted composition entrained in a stream of carrier gas as the thermoplastic composition is expelled from the applicator.
In a method according to the invention, the use of water as foaming agent leads to a number of advantages. It is a readily available non-toxic raw material which can be handled with ease using well known techniques and is substantially inert to commonly employed hot melts. It vaporises at a temperature compatible with temperatures commonly employed for application of hot melt adhesives and sealants and therefore does not impose severe requirements for heating as may occur, for example in the case of heat decomposable blowing agents. Also, by use of a method according to the invention, it is not necessary to mix a foaming agent with the composition prior to its supply and consequently one does not need to take steps to control or compensate for loss of foaming agent which may occur for example during manufacturing operations where heat is present or generated.
Thermoplastic compositions for use in a method according to the invention include those commonly used as hot melt adhesives and sealants especially those based on ethylene vinyl acetate copolymer or polyamides.
In one method according to the invention using an illustrative device hereinafter described, and using tap water at room temperature of about 20.degree. C..+-.2.degree. C., we have observed that, irrespective of the temperature to which the thermoplastic composition i
REFERENCES:
patent: 3174689 (1965-03-01), McIntyre
patent: 3362036 (1968-01-01), Swan et al.
patent: 3407151 (1968-10-01), Overcashier et al.
patent: 4066188 (1978-01-01), Scholl et al.
patent: 4259402 (1981-03-01), Cobbs et al.
Freudenreich Herbert
Hartmann Waldemar
Ritschel Peter
Brine Aubrey C.
Dawson Robert A.
USM Corporation
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