Froth system for continuous manufacture of polyurethane foam slab-stocks

Abstract

A process and a system for the continuous manufacture of polymeric foams. Reactive chemical components and additives comprising a low boiling blowing agent are mixed under pressure; the mixture is then frothed before chemical reaction takes place by feeding the mixture through a pressure equalizing and frothing device having a pressure-drop zone opening into a frothing cavity having an output aperture to discharge the froth onto a moving substrate.

What is claimed is:  
     
       1. A system suitable for the continuous production of polymeric slab-stock foam on a moving substrate comprising: 
       a mixing device for mixing reactive chemical components and liquid CO 2  blowing agent under pressure,  
       a feed line for carrying the mixture to a frothing device comprising a pressure equalizing chamber provided with a pressure drop zone dimensioned to maintain back pressure on the upstream mixture to keep the liquid CO 2 mixture in a liquid state and to initiate frothing under pressure controlled conditions to avoid turbulent evaporation of the blowing agent upon discharge of the mixture from the pressure drop zone, and  
       a frothing cavity having an outlet aperture extending transversely across the moving direction of the substrate and forming the discharged mixture into a progressively non-reactive expanding frothing material by progressively releasing the CO 2  in the frothing material as the frothing material flows along the frothing cavity.  
     
     
       2. A system for continuously producing low density, flexible polyurethane slab-stock foam on a moving substrate comprising: 
       a mixing device for mixing reactive chemical components and liquid CO 2  as a blowing agent under pressure;  
       a feed line for carrying the mixture to a frothing device comprising a pressure equalizing device provided with a pressure-drop zone dimensioned to maintained back pressure on the upstream mixture to keep the liquid CO 2 mixture in a liquid state and to initiate frothing under pressure controlled conditions to avoid turbulent evaporation of the blowing agent upon discharge of the mixture from the pressure drop zone;  
       and a walled frothing cavity extending from said pressure equalizing device, said walled frothing cavity being defined by walls that confine and permit the discharged mixture to develop into a progressively non-reactive expanding frothing mixture by progressively releasing CO 2  in the frothing material as the frothing material flows along the frothing cavity, and frothing cavity terminating at an outlet aperture for distributing an expanding frothing mixture onto and in the moving direction of the substrate.  
     
     
       3. A system according to claim  1  wherein said outlet aperture has a cross-sectional area greater than the cross-sectional area of said pressure drop zone. 
     
     
       4. A system as in claim  2  wherein said pressure-drop zone comprises an elongated slot. 
     
     
       5. A system as in claim  2  wherein said pressure-drop zone comprises a series of elongated slots. 
     
     
       6. A system as in claim  2  wherein said pressure-drop zone comprises a series of tubular outlet apertures axially extending in the direction of the flow. 
     
     
       7. A system as in claim  2  wherein said pressure-drop zone comprises at least one slot that axially extends and is elongated in the direction of the flow of material therethrough. 
     
     
       8. A system as in claim  2 , wherein said frothing cavity is defined by interconnected flow diverting wall means. 
     
     
       9. A system as in claim  2  wherein said walled frothing cavity includes walls that diverge in the direction of flow. 
     
     
       10. A system as in claim  2  wherein said pressure equalizing device comprises an elongated chamber. 
     
     
       11. A system as in claim  2  wherein said frothing cavity includes at least one substantially right angle turn downstream from said pressure drop zone. 
     
     
       12. A system as in claim  2  wherein the frothing cavity is proportional in its cross-sectional dimensions, in the direction of flow, to progressively release the frothing mixture. 
     
     
       13. A system as in claim  2  wherein the pressure drop zone extends transversally relative to the substrate, and wherein said outlet aperture has a greater cross-sectional area than said pressure-drop zone. 
     
     
       14. A flexible foam slab-stock plant comprised of a pressurized chemical mixing station for mixing polyurethane chemicals together with liquid CO 2  as a low boiling blowing agent with the mixture being maintained in a liquid state to produce a polyurethane foam material, a discharge assembly connected to said chemical mixing station for receiving the mixed polyurethane chemicals and for developing the mixture into a homogeneous progressively pre-expanding non-reactive froth material and depositing an expanding non-reactive froth material onto a substrate moving along a fall plate, and a conveyor assembly positioned relative to said fall plate for receiving the froth material discharged from said fall plate, said conveyor being operated at a rate of about 1 to 5 meters per minute so that the mixed polyurethane chemicals can react with full block height being achieved within a range of about 1 to 8 meters from the deposit point.