WO1990011179A1 - Production of foamed material - Google Patents

Abstract

In a foam forming process in which foam forming ingredients, e.g. for making polyurethane foam, are introduced (30) between or under a film cover, which expands to define a shaped block (40) as the foam forms while travelling, operational effectiveness is substantially improved by providing, upstream of the ingredients introduction point, means (7, 8) holding the film cover (1, 2) together in the direction of travel of the cover over a short distance, e.g. 3 to 8 cm, rather than, e.g. just bringing two films together in a nip between two rollers.

Description

PRODUCTION OF FOAMED MATERIAL

This invention relates to the production of foam material.

It is known to manufacture foam material by continuous processes in which foam-forming ingredients are fed together, the foam-forming reaction allowed to take place with the formation of a foam and in which the foam, as it forms and solidifies, is fed away in the form of a continuous block. European Patent Specification 0114741 describes such a process in some detail. In that specification, a method and apparatus are described in which the general direction of passage of the materials which come together to form the foam and the foam so formed is one of vertical upward movement. This has a number of advantages which are explained in the specification in question and in European Specification 0058553 and such vertical foam--forming methods have advantages, not least in terms of the space required for the plant to make them, over systems in which the foam-forming ingredients are cast on to a horizontally moving belt.

The apparatus described in European Specification 0114741 shows the introduction of foam-forming ingredients just above a nip formed between two pinch rolls, those rolls pinching between them a pair of opposed webs of flexible material between which the foam-forming ingredients are confined and, subsequently, the foam itself is confined. In practice, problems arise when attempting to carry out the process described in that specification arising from the nature of the foam-forming materials used.

As is well known, the components which need to be brought together to form a foam are highly reactive chemicals which present difficulties in handling, particularly in the case of those of them which are toxic. In particular, using the systems described in the European patent specification noted above, it is found very difficult to avoid the build-up of residual materials as foam forming proceeds, and eventually, often after as little as 20 or 30 minutes continuous forming, the plant has to be stopped, cleaned, and re-started. This is highly inconvenient and severely limits the output of such a plant. The problems can be particularly severe if the foam to be formed is a furniture grade foam resistant to combustion, e.g. so-called CMHR foam.

We have now found that substantial improvements may be achieved in foam-forming processes in which ingredients are introduced into a confined space between two flexible webs and then fed away from the point of introduction by movement of the webs, if the webs are biased together just prior to the point of introduction of the reactive materials over an area of contact which has an effective dimension in the direction of travel of the opposed webs. It is found that operating in this way, the build-up of materials can be substantially or wholly avoided and substantial continuous production runs effected.

According to a first feature of the present invention, there is provided a method of continuously manufacturing a foamed material which comprises feeding together a pair of opposed webs, feeding the opposed webs past a reactant introduction station at which liquid reactants are introduced between them and, following the introduction of the reactants, parting the webs while simultaneously allowing the reactants to expand to form the desired foam, the volume of the foam increasing as the webs are moved apart, characterised in that just upstream of the point of introduction of the reactants between the webs, the webs . are biased together over the whole of their width and over a longitudinal extent, measured in the direction of movement of the webs, sufficient to prevent the material build-up of residues at the reactant introduction station.

We have found that the biasing together of the webs in this way, as distinct from the line contact between the webs provided by the apparatus described in European Specification 0114741, leads to substantial improvements in operational practice with "no leakage" conditions being obtainable as well as the minimisation of residue build-up likewise being achievable.

The longitudinal distance over which the webs are pressed together may be varied, but usually it is desirable to press them together over a longitudinal travel of at least 1 centimetre, and preferably 3 to 8 centimetres. The webs may be pressed together for longer, but that leads only to greater engineering difficulties without leading to improved results.

According to a second feature of the invention, there is provided apparatus for the manufacture of foamed materials by a continuous process including means for bringing together a pair of opposed webs of flexible material at a foam-forming station, means for transporting the webs away from the foam-forming station while moving them apart from one another to define, as they move away, an increasing cross-sectional area of the space between them, and means for introducing into the space between the webs as they are parted a liquid foam-forming reactant mixture, characterised in that means are provided to bias the webs together over a distance of travel just upstream of the point of introduction of the liquid reactants to provide an area of contact (and not mere line contact) between them.

The means for producing the area of contact are preferably simple robust mechanical devices. We have found that a particularly simple apparatus for achieving this consists of a pair of opposed resilient faced bars, one either side of the web, the resilient facing extending by an appropriate amount, e.g. 3 to 8 centimetres, in the direction of travel, and the bars being held in a framework so they are pressed together.

In the operation of such apparatus, the liquid reactant mix must be introduced into the space between the webs and this is preferably done by injection means extending from upstream of the point of introduction to the point of introduction. In this way, there is nothing to impede the foaming and expansion of the mix as it passes away downstream from the point of introduction. The preferred mode of introduction is to introduce the ingredients through a flat nozzle over which the opposed webs of flexible material are drawn. Conveniently, a single nozzle is employed located in the centre of the webs and fed with ingredients from upstream. We have found that, because of the spreading ability due to capillary and suction action, the extent of the flat nozzle may be relatively small compared to the overall lateral extent of the opposed webs. For example, the nozzle itself may have an outlet opening only a few centimetres long and a few millimetres wide while the machine width may be 200 centimetres. The highly mobile nature of the reactant mixture nevertheless ensures good distribution across the entire machine width and even foam forming. A plurality of nozzles may be used with large machine widths.

Design variations may be made to the ingredients injection nozzle, for example by providing it with a short trough, e.g. 20 to 30 centimetres long from end-to-end which assists in enabling the reactant mix to move sideways. An alternative is to cap the top of an injection tube with a T-piece which diverts vertical flow up the vertical bar of the T to horizontal flows in two opposed directions from the ends of the horizontal bar of the T.

The nozzle may also contain diverter members to assist in turning the flow of the -liquid reactant mixture from a flow in an appropriate feed pipe in machine direction to lateral flow in cross machine direction into the narrow gap as it opens as the webs are drawn out from between the biasing members which extend across the entire machine width.

It is accordingly the case, when practising the present invention, that the foam-forming ingredients injection means, nozzle, trough, piping and the like, are relatively much smaller than the overall machine width (which can be as much as 2 metres or more). This enables a satisfactory transition of the shape of the reaction foam forming chamber between the point of ingredients injection and the final foamed block section to take place, to produce a foam of even cell size and substantially isotropic properties. In particular, the foam hardness measured in machine and cross-machine directions may vary from one another by less than 5% so that the orientation of the foam when it is cut to block form, e.g. for upholstery, does not need to be considered. It has been found in the case of commercial plants operating the system disclosed in European Patent Specification 0114741, that an ingredient spreading trough substantially of full block width is often needed, leading to constraints on the shape of the transition zone which in turn lead to foams where the hardness in different directions may vary, e.g. by as much as 20%.

Preferably, upstream of the biasing means which provide the area of contact between the webs, the webs are drawn together, e.g. by drawing them between a pair of opposed nip rolls. These nip rolls may be positively driven and assist in pulling the opposed webs together.

The opposed webs may be provided in the form of a continuous tube which is drawn from a shirred pack, but this is not generally preferred, particularly as the use of a shirred pack limits the length of a continuous run of production, and changing from one shirred pack to another on continuing production is a complex and critical process which cannot be achieved simply and guaranteeably with any ease. Layflat tubing may be used, but the preferred method is to bring together two separate webs, sealing them at their edges to form a continuous enclosure into which the reactant mixture is introduced. Such sealing may take place, e.g. by the use of an adhesive tape or by welding in the case of webs of thermoplastics material such as polyethylene. A particularly useful, flexible and economic way of making the tubing is to feed a plurality of webs of plastics film together adhering them at their edges using applied adhesive tape which may be adhered to one edge of the film so that it overlaps the edge and then brought into contact with the edge of another film. Both edges brought together may be pre-taped to form a joint with abutting or just overlapping plastics film edges with tape adhered across the join on both sides of each film. Following the formation of a stable foam, the web material confining the foam may be stripped off, the stripping away being assisted by fixed knives cutting the web or slitting the tape joins in it, and the web is then pulled away from the foam which then travels further, e.g. transported by pin conveyors, as described in the European patent specifications referred to above.

The important feature of the apparatus of the present invention is the means for generating an area of contact between the two opposed webs. This preferably consists of a pair of adjustable opposed members extending across the entire machine width and these members preferably consist, in each case, of a base member of a rigid fixed nature and a resilient faced bar, the biasing of the two resilient faced bars being adjustable across the machine width, e.g. by means of appropriate adjustment screws, levers, or the like enabling an even and controllable pressure to be applied to press the opposed webs into contact. An alternative construction which automatically provides a very even pressure is that of a rigid fixed member supporting an inflatable tubular member which may be pressurised to a different degree to adjust the operating conditions. The contact pressure should be sufficient to ensure adequate contact having regard to the need to prevent leakage but should not be such as to make it too difficult to pull the opposed webs through between the pressure bars. In order to reduce the pulling force needed, the pressure bars may be appropriately faced, e.g. with a low friction material such as polytetrafluoroethylene.

The method of operation and apparatus of the present invention may be used both in the case of horizontal foam manufacture where one of the webs is a horizontal run of a conveyor but its main area of application is in vertical foam-forming systems as described in the European patent specifications referred to above. It is found that using the method and apparatus of the present invention, there is very little or no tendency to the build-up of residues and substantial process runs may be obtained, e.g. lasting several hours or even longer. The transport of the foam block and its shaping may be achieved in known fashion, e.g. as described in the European patent specifications referred to above, and the output of the apparatus may be chopped in known fashion into blocks of convenient length for subsequent storage or processing.

The invention is illustrated in further detail with reference to the accompanying drawings in which:

Figure 1 shows a simplified diagrammatic side view of apparatus for producing foamed products,

Figure 2 shows a transverse section through the centre of the apparatus of Figure 1, on an enlarged scale,

Figure 3 shows a transverse section in a plane parallel to the section plane of Figure 2 but spaced from the centre of the apparatus, and

Figure 4 is an exploded view of the components of the apparatus just upstream of the injection station.

Referring to the Figures, two webs of polyethylene 1, 2 are drawn from respective stock rolls 3, 4 thereof and brought together at a nip between rollers 5, 6. They are welded or adhesively taped together at their edges (by means not shown) and pass upwards together into the space between two pressure bars 7, 8. Just above the pressure bars 7, 8 are located a pair of outwardly diverging conveyors 10, 11 which act to support the sides of the then tube of plastics film material which is drawn upwardly out of the nip between the pressure bars 7, 8.

The pressure bars 7, 8 consist, in each case, of a rigid bracket 20 extending across the entire machine width, having supported thereon a bar member in the form of a backing bar 21 on which is a resilient foam cushion 22 covered with a polytetrafluoroethylene fabric 23. The backing sheets are pressed towards one another by means of a series of bolts 25 which are screwed into the rigid members 20 and the two fabric covered surfaces of the pressure bars may be pressed more or less firmly towards one another by adjustment of these bolts.

The nip rolls 5, 6 may extend across the entire width of the machine but this is not necessary. The important requirement is to bring together the edges of the webs 1, 2 which are to be adhered together by welding, applied adhesive tape or other means. If full width rolls of plastics film are used, pairs of nip rolls 5, 6 each side of the machine may serve merely to bring the edges together to adhere adhesive tapes applied to the edges of webs 1, 2 into contact with the face of the other web.

This arrangement gives adequate space in the centre of the machine to accommodate an injection pipe 30 which, at its upper end, spreads out into a triangular fishtail shape 31 as it passes between the opposed fabric covered resilient cushioned bars. A short length of metal trough 32 is located at the upper end of the fishtail 31, this being set as shown at the point at which the opposed webs of polyethylene sheet 1, 2 are drawn apart. The width of the trough 32 across the machine is around 30 centimetres, the total machine width 200 centimetres. As is shown in Figure 3, across most of the machine width the polyethylene webs 1, 2 are fed together, brought into contact at their edges between the nip rolls 5, 6, pass together from there upwardly and into the space between the pressure bars 7, 8, then passing through between the pressure bars with webs 1 and 2 held firmly in contact. The webs are then peeled apart from one another as a continuously replenished bead of liquid reactant feeds along the parting webs as they form a tube in which the forming foam expands. The webs are drawn away upwards by. driven conveyor rolls 38 and, in the particular embodiment shown, these then pull the web away from the by then formed, but not yet cured, block of foam 40 which is fed further up by pin conveyors 41. Knives may be located at the ends of rolls 38 and of rolls at right angles thereto (not shown) to slit the polyethylene web and so facilitate its removal.

Pressure bars 7, 8 hold the webs together and provide a good seal at the base of the foam expansion chamber, minimising the risk of reactant escaping and running down the faces of webs 1, 2 below bars 7, 8. If desired, an auxiliary, e.g. temporarily inflatable extra pair of bars may be installed just below bars 7, 8, which may be used to push the webs together temporarily to assist in pulling any leaked material upwards and into the reaction chamber, so prolonging a production run.

The apparatus described may oe used for the manufacture of a wide variety of foams. In particular, the manufacture of normal high resilience polyurethane foams and of the more recently developed combustion modified high resilience (CMHR) polyurethane foams for use in upholstery may be manufactured conveniently and with long production runs using the present invention.

Claims

1. A method of continuously manufacturing a foamed material which comprises feeding together a pair of opposed webs, feeding the opposed webs past a reactant introduction station at which liquid reactants are introduced between them and, following the introduction of the reactants, parting the webs while simultaneously allowing the reactants to expand to form the desired foam, the volume of the foam increasing as the webs are moved apart, characterised in that just upstream of the point of introduction of the reactants between the webs, the webs are biased together over the whole of their width and over a longitudinal extent, measured in the direction of movement of the webs, sufficient to prevent the material build-up of residues at the reactant introduction station.

2. A method according to Claim 1, wherein the longitudinal extent over which the webs are pressed together is at least 1 centimetre, and preferably 3 to 8 centimetres.

3. Apparatus for the manufacture of foamed materials by a continuous process including means for bringing together a pair of opposed webs of flexible material at a foam-forming station, means for transporting the webs away from the foam-forming station while moving them apart from one another to define, as they move away, an increasing cross-sectional area of the space between them, and means for introducing into the space between the webs as they are parted a liquid foam-forming reactant mixture, characterised in that means are provided to bias the webs together over a distance of travel just upstream of the point of introduction of the liquid reactants to provide an area of contact (and not mere line contact) between them.

4. Apparatus according to Claim 3, wherein the means to bias the webs together comprises a pair of opposed resilient faced bars, one either side of the web, the resilient facing extending by an appropriate amount in the direction of travel, and the bars being held in a framework so they are pressed together.

5. Apparatus according to Claim 3, wherein the means . for generating an area of contact between the two opposed webs consists of a pair of adjustable opposed members extending across the entire machine width, each member consisting of a base member of a rigid fixed nature and a resilient faced bar, and means being provided for adjusting the biasing of the two resilient faced bars across the machine width.

6. Apparatus according to Claim 3, wherein the means for generating an area of contact between the two opposed webs consists of a pair of adjustable opposed members extending across the entire machine width, each member consisting of a rigid fixed member supporting an inflatable tubular member, and the apparatus including adjustable means to pressurise the inflatable member to adjust the operating conditions.

7. Apparatus according to any one of Claims 4 to 6, wherein the surface of the bar or tube in contact with the opposed webs is faced with a low friction material such as polytetrafluoroethylene.

8. Apparatus according to any one of Claims 3 to 7 and including injection means for introducing the liquid reactant mix into the space between the webs extending from upstream of the point of introduction to the point of introduction.

9. Apparatus according to Claim 8, wherein the liquid reactant mix is introduced through a flat nozzle over which the opposed webs of flexible material are drawn.

10. Apparatus according to Claim 9 and including a single nozzle located in the centre of the webs and fed with ingredients from upstream.

11. Apparatus according to Claim 9 or 10, wherein the extent of the flat nozzle is relatively small compared to the overall lateral extent of the opposed webs.

12. Apparatus according to any one of Claims 9 to 11, wherein the flat nozzle terminates in a trough extending to both sides of the nozzle.

13. Apparatus according to any one of Claims 9 to 12, wherein the nozzle contains diverter members to assist in turning the flow of the liquid reactant mixture from a flow in an appropriate feed pipe in machine direction to lateral flow in cross machine direction into the narrow gap as it opens as the webs are drawn out from between the biasing members which extend across the entire machine width.

14. Apparatus according to Claim 8, wherein the liquid reactant mix is introduced via an injection tube, the top of which is capped with a T-piece which diverts vertical flow up the vertical bar of the T to horizontal flows in two opposed directions from the ends of the horizontal bar of the T.

15. Apparatus according to any one of Claims 3 to 14 and including, upstream of the biasing means which provide the area of contact between the webs, means for drawing the webs together.

16. Apparatus according to Claim 15, wherein the means for drawing the webs together is a pair of positively driven opposed nip rolls.

17. Apparatus according to any one of Claims 3 to 16 and including means for providing the opposed webs in the form of a continuous tube which is turned by bringing together two separate webs and sealing them at their edges to form a continuous enclosure into which the reactant is introduced.

18. Apparatus according to Claim 17 and including means for feeding a plurality of webs of plastics film together and adhering them at their edges using applied adhesive tape which may be adhered to one edge of the film so that it overlaps the edge and then brought into contact with the edge of another film.