Method and apparatus for producing a foam from a viscous liquid

A method of producing a coherent output stream of liquid adhesive containing a dispersed gas which after discharge will expand to form a foam, comprising,

• pumping the liquid adhesive, under several hundred pounds pressure, as an integral stream into a chamber,
• separately introducing a gas into said chamber at a pressure greater than said adhesive, through passages having minute openings to said chamber that are swept by the stream of the pressurized adhesive, the flow of liquid across said openings segmenting the gas entering therefrom as microbubbles entrained in the stream, thereby forming an unstable gas/liquid mixture,
• conveying the mixture to a discharge orifice which is adjacent the chamber, without further pressure increase but while maintaining sufficient pressure on the mixing so formed to prevent pre-expansion of said gas during such conveying, and
• abruptly reducing the pressure by expelling the mixture to atmosphere through a restricted discharge orifice,
• the mixture exiting the discharge orifice as a stream in which said microbubbles then expand to form a foam.

A method of foaming a viscous liquid which comprises:

• supplying a viscous liquid to a chamber of an applicator at a first pressure which is substantially above atmospheric pressure,
• causing said liquid to flow through the chamber as an integral stream,
• supplying a gas to said chamber at a second pressure which is above the first pressure,
• delivering the gas into the integral stream of the liquid, the movement of the liquid stream through the chamber segmenting said gas into microbubbles in the liquid,
• further dispersing said microbubbles in the liquid by providing static mixing in a tortuous flow path,
• delivering the dispersion of the microbubbles in the liquid from said chamber to a restricted outlet orifice which is close to and in communication with the chamber, said delivery to the orifice being effected without mechanically increasing the pressure of the dispersion, and
• releasing the dispersion to the outside of said applicator from said chamber through said restricted orifice as a stream which is coherent in passage to a substrate, whereby a foam will be produced on said substrate.

Apparatus for foaming a viscous liquid which comprises

• means for pressurizing the liquid to several hundred pounds pressure and delivering it under pressure to an applicator having an internal chamber wherein it is mixed with gas,
• said chamber presenting an internal flow space for the flow of said liquid therethrough as a continuous stream,
• passage means for introducing the gas under pressure into said liquid in said chamber through minute transverse openings to said chamber past which the liquid flows as a continuous stream, to form an unstable mixture of the gas and the liquid,
• means for maintaining the gas and liquid mixture under pressure but without further pressure increase while it is conducted from said chamber to an orifice, and
• said orifice being a restricted outlet orifice close to the chamber for dispensing the gas and liquid mixture to atmosphere as a coherent stream.

Apparatus for foaming a viscous liquid which comprises

• means for pressurizing the liquid to several hundred pounds pressure and delivering it under pressure to an applicator having an internal chamber wherein it is mixed with gas,
• said chamber presenting an internal flow space for the flow of said liquid therethrough as a continuous stream,
• pressure means for introducing the gas under pressure into said liquid in said chamber through minute transverse openings to said chamber past which the liquid flows as a continuous stream, to form an unstable mixture of the gas and the liquid,
• means for maintaining the gas and liquid mixture under pressure but without further pressure increase while it is conducted from said chamber to an orifice,
• said orifice being a restricted outlet orifice close to the chamber, for dispensing the gas and liquid mixture to atmosphere as a coherent stream, and
• a flow restrictor which is adjacent said openings to said chamber, said restrictor comprising a capillary tube having an axial bore and a wire extending into said bore, an annular flow space being defined around said wire in said bore.

A system for producing a coherent output stream of liquid adhesive containing a dispersed gas which will expand to form a foam bead, comprising

• a source of liquid adhesive under several hundred pounds pressure,
• a liquid conduit connected to said source,
• a contacting chamber communicating with said liquid conduit for flow of said liquid adhesive therethrough,
• a source of gas under pressure greater than the liquid pressure,
• a gas conduit connected to said gas source,
• said gas conduit including a gas flow restrictor,
• said flow restrictor positioned closely adjacent said chamber and communicating with it through minute gas injection openings across which the liquid adhesive stream flows, and
• passage means leading from said chamber directly to an adjacent discharge orifice, said discharge orifice being a short, restricted orifice having a length to diameter ratio which is less than 1.

An attachment mountable to a hot melt adhesive dispenser to adapt it for producing a coherent output stream of hot melt adhesive containing a dispersed gas which will expand to form a foam,

• said dispenser being of the type including a body, a delivery passage through which said adhesive is delivered under high pressure, and a valve for controlling delivery of said adhesive through said delivery passage, said attachment comprising,
• a head mountable to said body for dispersing a gas in said adhesive in the head,
• a contacting chamber communicating with said delivery passage and through which said adhesive flows as an integral stream,
• a gas conduit for connection to a source of gas under pressure, said conduit including a gas flow restrictor,
• said flow restrictor positioned adjacent said chamber and communicating with it through minute laterally disposed gas injection openings across which the adhesive stream flows in a generally axial direction, and
• passage means leading from said chamber directly to a discharge orifice close to said chamber, said discharge orifice being a restricted orifice having a length to diameter ratio which is less than 1.

An attachment mountable to a hot melt adhesive dispenser to adapt it for producing a coherent output stream of hot melt adhesive containing a dispersed gas which will expand to form a foam,

• said dispenser being of the type including a body, a delivery passage through which said adhesive is delivered under high pressure, and a valve for controlling delivery of said adhesive through said delivery passage, said attachment comprising,
• a head mountable to said body for dispersing a gas in said adhesive in the head,
• a contacting chamber communicating with said delivery passage and through which said adhesive flows as an integral stream,
• a gas conduit for connection to a source of gas under pressure, said conduit including a gas flow restrictor,
• said flow restrictor positioned adjacent said chamber and communicating with it through minute laterally disposed gas injection openings across which the adhesive stream flows in a generally axial direction,
• said flow restrictor comprising a capillary tube having an axial bore and a wire extending into said bore, an annular flow space being defined around said wire in said bore, and
• passage means leading from said chamber directly to a discharge orifice close to said chamber, said discharge orifice being a restricted orifice having a length to diameter ratio which is less than 1.