Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1998-03-30
1999-12-21
Cooney, Jr., John M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
264 459, 264 50, 264 51, 2641761, 264211, 26421121, 425 4R, 425 4C, 425190, 521 80, 521917, C08J 904
Patent
active
060050144
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an apparatus and process for producing polymeric foam and in particular, but not exclusively, to an apparatus and process for the continuous production of low-density polymeric foam.
The preparation of polymeric foams has conventionally required the mixing or several components which react to form a foamed polymer. Typically, the components include a polyol, an isocyanate, a catalyst or catalysts, a surfactant and water. When these components are mixed together in the correct proportions, the water reacts with the isocyanate to produce carbon dioxide for expansion of the polymer.
By discharging a layer of the mixture onto a moving conveyor (with a movable base and with adjustable opposed side walls) the components of the mixture react and continuously produce a polymeric foam.
More recently, the continuous production of low density foams has involved the use of a relatively inert, low boiling point liquid which is mixed under pressure in a liquid state with the other chemical components in order to provide an auxiliary blowing action on the mixture before the mixture expands by production of carbon dioxide from the isocyanate/water reaction. The mixture is discharged onto the conveyor and the vaporised low-boiling point liquid expands the reaction mixture which then subsequently expands by the chemical production of carbon dioxide from the reaction mixture to form a polymeric foam.
Suitable blowing/frothing agents include the various chlorofluorocarbons (CFCs). Although CFCs have the desired inertness and relatively low boiling point, their use has recently been discouraged on environmental considerations since it is believed that CFCs contribute to depletion of the ozone layer. A suitable replacement for CFCs is carbon dioxide but since carbon dioxide vaporises at a much lower temperature than CFCs, and indeed must be pressurised in order to exist as a liquid, relatively high pressures have been maintained throughout the apparatus and method.
However, unless the vaporisation of the carbon dioxide occurs under controlled conditions, some of it can be lost and the efficiency of the foam expansion is reduced and poor quality foam may be produced, with non-uniform cell structure and voids or "pin-holes".
The apparatus described in EP-A-0645226 attempts to discharge the reaction mixture under controlled conditions by discharging the mixture through an elongate pressure-drop zone to initiate frothing, flowing the frothing mixture along a frothing cavity and through an outlet aperture and subsequently discharging the frothing mixture onto a substrate.
In published WO 96/00644, it is proposed to expand a foamable reactive mixture into a large number of individual flows at shear rates of above 500/sec. This is sought to be achieved by passing the reactive mixture through one or more separate fine meshed screens having a screen size from 0.025 to 0.3 mm. The "screens" envisaged in WO 96/00644 comprise apertured discs or nets, ie. having simple direct paths therethrough. The various embodiments shown by way of example in WO 96/00644 all use separate, multiple fine-meshed screens which are held apart axially by respective spacers so as to have a clear space therebetween. This appears to have the likely disadvantage that, due to the individual pressure drops across these screens, some foaming is likely to take place in the spaces between the screens which would be highly undesirable in practice.
The "reactive mixture" which is used in the technique disclosed and claimed in WO 96/00644 is obtained, using at least two reactive components and carbon dioxide as expanding agent, by mixing at least one of the reactive components with carbon dioxide under pressure, thereby producing a mixture containing liquid carbon dioxide, and then mixing the resultant mixture with the other reactive component to form the foamable reactive mixture. The latter mixing steps are typically carried out in a static mixer and rotary mixing head, respectively.
The latter system relies on having a fully mixed "reac
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Blackwell James Brian
Blackwell John James
Blackwell Stephen William
Buckley Geoffrey
Beamech Group Limited
Cooney Jr. John M.
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