CA1176416A - Production of foams - Google Patents

Abstract

ABSTRACT A method of continuous upwards production of foamed material by feeding foam forming materials from below and taking foamed material away from above, wherein foaming takes place in a diverging expansion enclosure the walls of which are provided with surfaces travelling with the foaming material, which enclosure is defined above by foam already expanded, at the sides by said walls and below by a feed zone for the foam forming materials, and leads into an upwardly directed take off path for the foam.

Description

~7~6 PRODUC_ION OF FOAMS

F LD OF INVENTION

The invention relates to the production of foarned materials and in particular of polyurethane and other polymer foams, in terms of which it is largely described.

PRIOR ART METHOD

Expanded rr~terials, particularly polyurethane foams, are Tr~de in both batch and continuous plant.
Batch production may be at any desired rate to suit subsequent conversion but is inherently labour intensive, can give variation from block to block, and is wasteful in giving blocks where all six sides are skinned and need trirr~ning. The blocks, foamed in moulds, also show undesirable densification at the corners, which the rising and steadily more viscous material has to be forced to occupy by a weighted, floating cover or other means Continuous production as currently practised also has major d;sadvantages. The conventional, horizontal machines have inherent characteristics of large ~ize and h;gh rninimum prod~lction rate, arising Erom the nature o the ~oarning reaction and the newly formed foam, and the curing time needed before material can be handled. This curing time, typically 5 to 15 minutes Eor polyurethane, sets the length oE the plant once the rate of travel oE
the conveyor that carries the Eoamed ~lterial is determined.
This rate of travel in turn depends on the height of the ~P

- 2 - ~7~6 block required, only a certain steepness of profile being supportable by the material in the early stages of foaming and setting. An over-steep profile gives problems of underrun by dense, unfoamed material, or of slumpinq of unsupported newly foamed material, or both.
The conveyor must travelfast enough to maintain -the proper profile, giving a minimum production rate of for example 100 - 200 kg/min for 1 metre high polyurethane blocks, and thus a machine length of 40 to 50 metres.
Any attempt to reduce the speed of the conveyor to give a lower production rate and hence in principle a shorter machine steepens the profile and causes underrunning or slumping, or both, making production of a uniform block impossible. Large machines thus have to be installed, at heavy capital cost, only to remain unused for muah of their time.
Further features of known machines will be described with reference to the accompanying drawings which also show embodiments of the invention, and in which:-Figs. 1 and 2 are diagrammatic drawings showing operations with known prior art machines;
Fig. 3 shows a general vlew of a complete machine in accordance with the invention;
Fig. 3A shows paper folder details;
Figs. 4A and 4B show the machine in two vertical sections at right angles -to each other;

~t7~ 6 - 2a -Fig. 5 shows an expansion enclosure;
Figs. 6A-6E show density profiles for foam blocks made in ~hree conventional inclined-conveyor machines as referred to in relation to Fig. 1, using top papers to con-trol top skin formation and improve block shape (Figs. 6A, 6B, 6C); a conventional machine with trough and fall plate and a free -top surface as referred to in relation to Fig. 2 tFig. 6D~; and the machine of the invention (Fig. 3) operated as described in Example 1 herein;
Fig. 7 is a plot of the combined volume of the feed zone and expansion enclosure ~up to the parallel section) of the last referred to machine; and Fig. 8 is a rise profile from a box pour of the materials used in Example 1.
The limiting factors of known machines are illustrated in Figs. 1 and 2 which show two known kinds of machine for foaming polyurethane, the first (Fig. 1) having li~uid reactants fed direct to a sliqhtly sloped conveyor (about 6 to the horizontal) and the second (Fig. 2) having the reactants fed to a trough, from which they spill over in the first sta~es oE reaction onto a eall plate leading to a horizontal conveyor~ Such machines are described in some detail ln for example U.S. Patents Nos. 3,325,823 to D.J. Boon and 3,786,122 to L. Berg.
The foam profile in the machine of Fig. 1 is approximately as shown at 'B', determined by the rate of feed reactants at 'A' and the rate of travel of the

-3-conveyor. The boundary between closed-cell foaming material and o~en-cell rnaterial after gelling and breathing is shown at 'C', the breathing zone being marked ID'. Cut-off is at 'E'. The rate of travel has a certain minimum, since while to avoid slumpîng, on running more slowly, a more steeply inclined conveyor would in theory steepen the profile with respect to the conveyor but leave the effect of gravity unaltered, the liquid reactants fed at 'A' would then underrun the foamlng mass~
In the machine of Fig. 2 the risk of underrun problems has been reduced by conducting the first stages of reaction in the trough and feeding the resulting creamy and already somewhat viscous reacting mass to the fall plate 'Fg.
There is still however a profile 'Cl between closed-cell fluid froth and open-cell newly gelled material, which cannot be steepened by reducing the conveyor speed and hence production rate without danger of slumping and thus loss of u-niformity in the resulting block.
The difficulties with these rnachines are felt onLy when full size foam blocks at production rates below 100 - 200 kg/min. are required, but it is in fact only the very largest producers that can use capacity of that order.
Many rnachines are as noted run only for an hour or two a day, the user spending the rest of the day handling the resulting foarn. A typlcal smk~ll foamer producing say 2000 tons or less o Einished foam annually might want production at 10% of the above rate for econornic operation, and cannot accept the storage and handling problerns of large yuantities of foam and the cost and space requirements

-4-of a large machine. Even middle range producers who can accept the big mach;nes, with their disadvantages, would be better served by machines of lower production rate.
There is therefore a potential dernand, hitherto unsatisfied~ or a continuous-production machine capable of running at for example lO to 50 kg/min producing polyurethane foam~ that is to say levels conven;ent to a typical small foamer's production.

~` THE PRINCIPLE OF THE INVENTION

We have now found that if -the principle of existing machines is abandoned a low production rate machine can be provided. The invention stems from a realisation that horizontal production is unnecessary and that in a suitably designed machine foam can be drawn away upwardly rather than horizontally, withou~ interEerence with the foaming reaction.

SPECIFIC PRIOR PROPOSAl.S
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Proposals have in fact been made for the continuous upward production of foam, in West German Patent Specificatiolls Nos. 1 169 648 (Munneke) an(l 1 504 091 (Continental G~ ni-Werke), and in East Gerr~n Patent Specification No~ 61613 (Berbig), b~lt we know of no practical applicat-lon of these proposals. It appears that problems of control of the reaction and prodllction o a uniform product had not been solved by the proposals as described, so that Eor all their disadvantages the large horizontal machines have been in extensive commercial use. Berbig is a generalised disclosure giv;ng no process details or other indication that it was even run, and Munneke is the same. Moreover he shows a flat-botto~ed reaction chamber of a type impossible in our experience to feed uniformly with the foam forming material. Even the most detailed of the three disclosures, that by Continental Gummi-Werke, does not recognise any difEiculty in relating the machine construction to the stages of the foaming reaction to secure uniformity in the finished foam.

`. STATEMENT OE' INVENTION
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We have found that for successful continuous upwards foam production, it is necessary that foaming takes place in a di~7erging expansion enclosure the walls of which are provided with surfaces travelling with the foaming material, which enclosure is defined above by foam already expanded, at the sides by said walls and below by a feed zone for the foam forming materials, and leads into an upwardly directed take off path for the foam. Curing can occur, or at least begin, in the take off path.
As explalned ln detail later herein, the essential lles in the provision of the travelling surfaces in the expansion enclosure.

FOAMING
___ The greater part, though not necessarily the whole, of the foaming takes place in the expansion enclosure.

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Specifically, it will be appreciated that as the feed zone and expansion enclosure are contlnuous with each other, and the division between the two is regarded as where the travelling surfaces begin, foaming can start in the feed zone. Then, the foaming material contacts the travelling surfaces at an intermediate stage of reaction~
The latest satisfactory intermediate stage will vary with the kind o foaml but in all ordinary cases the s-~ratum of the foaming rnaterial in which contact with the travelling surface is made will be less than 5QV~o expanded in terms of the volume change from initial foarn forming rr~terials to finished foam. More usually the rnaterial will be less than 40% and often less than 30% or even 20V,~ expanded.
The position in the machine of the stratum of a given degree of expansion is calculated from the free foam rise profile in a box test on a batch of the material, taken with the feed rate of fresh material to the rnachine, by summing the volumes reached by notional successive srnall volumes of material during their individual residence times and relating the sum to the combine~ volume of the Eeed zone and expansion enclos~re of the machine up to a given height.
Examples of these calculations are given in detail later herein, The clegree of expansion oE the rnaterial, determining increasirlg viscosity and eventual gelling of materials such as polyurethane, is thus related to the latest suitable position for take up on the travelling surfaces.
The increasing slowing of material that occurs adjacent to stationary walls as viscosity increases is countered, and holding back oE material at the walls leadlng to gelling thereon does not occur. On the contrary,a srnooth flow is maintained and blocking of the flow or interrnittent loss of lumps of gelled m~terial giving non-uniform properties in the product avoided.

EXPANSION ENCLOSURE

The expansion enclosure diverges (in the sense of having increasing cross sectional area) over the greater part -though not necessarily the whole of its volume. Thus it may both begin and encl, and conveniently does at least end, with a non-diverging section. The former may arise lf the travelling surfaces are brought in early, lower than the level at which expansion of the foam mix co~nences. The latter is convenient to allow for control tolerances during a run, so that completion of expansion does not have to be matched exactly to the cross-section and there is no danger of expansion being insufficient and leaving a gap of varying width between the expanded mass and the enclosure walls.

TRAVELLIN_ SURFACES

The speecl of the travèlling surfaces need not be the same as the translational speed of the foaming Inix adjacent to them7 though clesirably the two speeds approximate. It will be appreciated that where for example a rectangular section expansion enclosure has two opposite parallel walls and the clivergence of cross section is provided by the other two walls, webs of paper or plast-;cs drawn over the ~ ~ 7 ~

diverging walls to provide the travelling surfaces cannot match the speed o the enclosed material both in the diverging and in subsequent parallel portions of the path of the material.
Thus in the above way the whole body of material is kept moving during expansion reducing eddy or river bank effects, preventing development of gelled or solidified material on the enclosure walls, and ensuring tha-t tnaterial at any given stage of expansion is essentially in the same horizontal plane throughout and that a uniform body of foam is produced. In polyurethane foam production for example, the boundary between still-liquid and gelled tnaterial is horizontal or essentially so~ uninfluencecl by - gravity. Underruns or slumping as discussed earlier cannot arise, and any convenient production rate can be adopted with a maximum depending on the length o~ the material path and thus the dwell time it gives. There is in the foam produced an i-nherent uniformity of properties, the 'gravity history' of all parts of the block being the same, STATEMENT OF INVFNTION - PLANT

The invention further provides plant for the contimlous upwards production of foam, cot~prising a eed zone opening into a diverging expansion e-nclosure, means for feeding Eoam forming materials to the feed zone, and a take oEE
path for foamed tnaterial opening from the enclosure, the enclosure having walls provided with surfaces thak travel with the ~oaming tnaterial.

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DEFINITIONS

The invention is in principle applicable to the production of foamed rnaterials of all kinds, but more specifically to expanded and in particular chemically expanded polymer foams. 'Cure' is any chemical or physical process by which newly formed foam becomes handlable, and Ireaction' any process by which gases expanding the foaming ; material are developed.

FEED ZONE AND EXPANSION ENCLOSURE CONSTRUCTION

If achievable without serious sealing problems the whole expansion may as noted take place in contact with travelling surfaces, when the feed zone will be srnall, but for materials such as polyurethane foams, where the initial reactant mix is a thin searching liquid difficult to seal, it is preferable for the feed zone to ~e defined by an open topped vessel fed continuously from below with the foam forming rnaterials, the travelling surfaces being introduced where this vessel adjoins the walls of the expansion enclosure. Such a vessel can readily be dimensioned to allow Eor Eirst stage of for example a polyurethane foaming react;on to talce place in it, a crearny anA already somewhat viscous l~terial pass;ng to khe expansion enclosure proper, The shape of the expansion enclosure and feed zone is a matter of convenience but is generally such that the increase in volume in the direction of travel of the foaming material is rnatched to the expansion curve of the reacting material. There is then a substantially constant speecl of upward travel in the mass of foaming material.
Conveniently the feed zone is in the form of a horizontal channel defined by walls continued at the sides by diverging walls and at the ends by parallel walls of the expansion enclosure between which the side walls lie.
Such a construction, giving a generally wedge shaped expansion enclosure, lends itself to a variable expansion enclosure geometry~ for example by pivoting or flexing the diverging walls, and hence to ready variation in block size while the plant is running by correspondingly moving out the walls of the ~ake off path. It is Eurther possible to have the diverglng walls and feed channel telescopic, to allow the depth as well as the width of the block produced to be varied.

PAPER AND PLASTICS WEBS

The above construction also lends itself readily to the drawing of travelling webs of material such as paper or plastics over supporting wall surfaces, the preferred method of providing the travelling surfaces. A paper web for example, folded ro~md at the sides so as to give a lap applied to the back of such walls, readily follows their shape when clrawn through from above, even if the shape is somewhat curved, without lifting off and without creep;ng over the wall edge. Stability is enhanced if the edges oE the diverg;ng walls have a longitudinal rib or bead over which the paper passes, and especially if a non-extensible tape is applied down the back of the paper near the edge of the wall (next to the bead if used).

PRESSURE MONITORING

An important factor in foam production for safety and consistent cell structure, certainly with polyurethane, is control of the pressure within the foaming mass. Since an inherent feature of the upwards foaming concept is that the expansion stage must be conducted in an enclosed vol~me, and since chemical reactions are prone to variation in rate due to such factors as temperature, degree of mixing of reactants, and impurities, provision for control of and pressure in the expansion enclosure is desirable. It is readiiy provided by, for example, a pressure transducer in the feed zone wall or any other position where the foaming mix is still liquid, and control of feed or take off -~ccordingly.
In general however it is sufficient to observe the pressure as remaining within safe limits and at a small positive figure. The gelled foam in reaction such as the production of polyurethane cannot then be pulled away from the ungelled still liquid foaming materials below~ A
suitable pressure is for example 10 to 30 mm/Hg gauge~

CONTROL BY FEED AND TAKE OFF RATES

Actual control is then by matching the take of rate of the volume of Eoam of a given density with the feed rate of volume of reactants of a given density (allowing for any reaction loss of materials that do not appear in the finished foam~. As noted earlier it is irnportant that the expansion should not have been completed before the foamed material leaves the diverging part of its path.
If it shows a tendency to do so, either the tota]
throughput can be increased, or the reaction rate at a given throughput can be slowedj for example by lowering the temperature or the catalyst concen-tration. Clearly for a fast reacting foam a srnaller expansion chamber is needed at a given speed of removal of finished foarn than for a slow-reacting one, as less time is occupied between introduction of the materials and their full foaming and thus less volume of f;nished foam will have been ~aken off ; in that time. If a given expansion enclosure is proving too large therefore, slowing the reaction will compensate~
In practice a given expansion enclosure volume can be selected, a throughput chosen, considering in its simplest terms weight of reactants in and weight by volume of foam out, and fine control exercised by catalyst or temperature variation, the position of the full-foaming profile moving up or down according to the reaction rate.

INCLINED PATHS

The upwards expansion and movement of foamed material is conveniently vertical, but a path inclinecl from the vertical will serve provided that during exp~msion material at earlier stages of expansion and thus of higher density rer~ains below material at later stages of expansion and thus of lower density. It rnay be advantageous to have an -inclined path if, as discussed below, conveyors with pins are in use. The weight of the material will assist engagement with the pins on one conveyor as well as the weight being partly taken direct on that conveyor, while still allowing engagement of the pins on the other conveyor with the opposite face of the block. T~e path of expansion and movement of the foamed material will further norrnally be straight, but with a flexible foam a change of direction may be made if required once the foam has developed suff;cient coherence.
A large arc will be required3 but will give the'possibility r for example of long lengths of foam for joining end to end '~ and use in the manufacture of sheets by 'belt~ peeling.

POSITIVE TAKE O~F
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Ordinarily, to avoid interference with the foam production by a weight of foamed rnaterial above, the foamed material is positively drawn away, conveniently by a conveyor defining a closed path for it, but this is not an essential of the invention. A conveyor rnay not be needed, and further the path of the foamecl rnaterial may not ; 20 need to be enclosed (unless to retain heat) once foaming is complete (in the case of polyurethane or other open-celled foam once 'breathing~ has ta'ken p'Lace) and the material has cured sufficiently to be self supporting.
PreEerably however, to reduce frictional effects, the path of the foarned materials is definecl after as well as during foaming by moving suraces. These surfaces may act throughout as conveyors, and indeed, once the foam has developed sufficient strength to sustain tensile forces, w;ll certainly do so where there is adhesion between the Eoam and the surface. Adhesion of the foam may be sufficient alone where a conveying action ;s re~uired, but, according to the strength of adherence oE the foam to the surfaces and the nature of the materials, positive engagement as by pins or other means may be provided on one or more of the surfaces.
Pins of convenient length for polyurethane foam for example are about 1 cm, spaced laterally 5 cm apart and vertically 5 cm apart, though there is no restriction to any particular spacing or length or distribution of pins.
~ Pins of such length (1 cm) enter only the thickness of the ; block that is normally ski~ned off to clean up the faces, but in any case damage by the pins to the block is generally negligible.
As noted above, a conveyor may rely on adhesion of the formed body of foam, or if required may positively engage it, for example by the pins referred to, which take hold of the foam once it has developed sufficient strength.
The conveyor surface, a travelling web of release paper or plastics film as well known per se in horizontal machines, may then be penetrated by the pins as it is fed.

VAR rA~:rl ON OF BLOCK SIZE

It will be .apDrec;ated that the block size is not limited by the foam rise as in horizontal machines. Any block wLthin the limits of s-;ze deined by the expansion enclosure and take oEf path may be produced. This size may in itself be varlable if provision ;s made for varying . . .

., the separation of opposed parts of the expansion enclosure or otherwise varying the path cross section.
For example as already mentioned the bottom edge of the side walls of the expansion enclosure ~ay be pivoted and the corresponding walls of the take off path moved in and out to match, and/or telescopic side walls ~and feed cha~mel or the like) may be used and the end walls moved in and out. This is a valuable feature for machines of rnoderate output such as the invention gives, allowing small runs of various sizes of block.

A preferred shape for the expansion Pnclosure is as discussed earlier a wedge opening into a rectangular (or - square) path for the formed oam. A feed zone, in the form of a channel to which foam forming materials are fed can then conveniently be placed at the base of the wedge and the main faces or sides of the expansion enclosure can readily be made adjustable as referred to above to give a variable included angle and hence block size. The length of and dwell time in the expansion chamber can, further9 suit the particular mk~terial being foamed and the production rate in use.

ALrERNATIVE EXPANSION ENCLOSURE CONSTRUCTIONS

The walls of the expansion enclosure are conveniently flat or shaped metal or like plates, but flexible members can also be used, particularly for diverging walls. The ~L~ 6 length Can then for exarnple be adjustable by altering the separation of end rollers or other guides over which the flexible rnembers pass. Conveniently a continuous belt is used, one or more jockey rollers or like guides taking up excess. Ordinarily the belts will be moving~
conveniently fed with a release paper or plastics film web as with the fixed walls referred to earlier.
The travelling surfaces at the diverging sides of a wedge-shaped expansion enclosure with either fixed or flexible walls can if so wished move at a greater speed than a conveyor carrying the formed foam away, according 3 to their inclination to the main direction of flow, when il all 'river ban~' effects in the movement of the material are avoided. Separate travelling webs can readîly be ;~ 15 provided to achieve this, but as already noted, such ; provision is not essential and it is in fact convenient to draw webs away from the top of the machine, to avoid a multiplicity of feeds and rolls.

SEAL~NG EXPANSION ENCLOSURE

To seal corners against leakage of materials where the sides of the expansion enclosure meet, close contact should be maintained, and this is readily possLble w~lere for example wrap-round webs of paper or the like are used as descrLbed. Alternatively it may be expedient to Eeed a release paper or plast:Lcs film in such a way that it laps in~side the corners onto the face oE an engaging member of the expansion enclosure~ so that the pressure of foam forming materials or newly formed foam engages the lap and enhances the seal. ~lere feed zone and expansion enclosure meet, a flap of flexible plastics lapping onto the incoming webs providing the travelling surfaces gives a good seal.

ALTERNAI'IVE BLOCK SHAP_ The body of oam produced as described above is conveniently rectan~llar or square but there is no limitation to that shape In particular, round blocks can be made with a su;tably shaped feed zone, expansion enclosure and take o~f path, for direct use in the production of foam sheet by the 'peeling' process. Any prismatic or indeed rounded form may be produced 'by an appropriately shaped and if re~uired sectional expansion enclosure and take off path, fed with as many separate '15 webs of release p~per or plastics film as may bP
con~enient. For circular section blocks, a convenient expansion enclosure is conical, formed e.g. of two or more sections fed with release paper or plastics film webs guided to enter where the feed zone meets the expansion enclosure. Where they enter, such webs are largely external of the expans;on enclosure~ folded back through gaps between the sections, but as they pass up the enclosure the excess is 'Largely drawn inO Feed problems are not serious at the low rates of travel requ;red.

THE DRAWINGS
, ~he following detailed description with reference to ~i~s~.
3 to 8 of the drawings is by way oE

example of the invention.
The machine shown may be used for example for flexible polyurethane, rigid polyurethane, polyisocyanuarate, . ureaformaldehyde, phenol-formaldehyde, silicone and epoxy ; 5 based foams but are described in relation to the first of ` ~
these.

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DETAILED DESCRIPTION OF MACHINE OF FIGS. 3 TO 5 In the machine as shown in Figs. 3 to 5 an expansion enclosure 1 ]ies below a take off path defined by opposite fixed walls 2 and spiked slat conveyors 3. The machine is built on a frame (not indicated~ with an access stair to a central ~latform and a top platform. A generally conventional inclined-path cut-off saw (giving a square cut) is provided at 6, to sever blocks 7 (Fig. 43 from the rising foam body 8, which blocks are tipped on~b a conventional roller conveyor at the top right of the machine as seen in Fig. 3.
At one side of the maohine is a generally conventional mixing head 10 delivering to a feed channel 11 by means of two delivery pipes 12. The feed channel lies between the lower edges of two curved expansion-enclosure side walls, the edges of which are indicated at 13, and two end walls 14. The side walls end at the take off path walls 2, and the end walls 14 at the slat conveyors 3.
In the expansion enclosure and take off path moving surfaces are provided on the end walls by means of polyethylene webs 15 fed from rolls 16 and drawn round the lower edges of the end walls 14 by the conveyors 3. The webs remain on the end faces o the foam blocks produced.
The moving surfaces for the curved side walls of the expansion enclosure are provided by paper webs 17 fed from rolls 18 and dra~n through the mkachine by powered pinch rolls 19' (Fig. 4A) to take-up rolls 19, separating them from the side faces of the block. The paper webs pass ; once through the machine and are scrapped ater use.

~7~Lf~

The slat conveyors and pinch rolls are synchronised by a common drLve below the top platform, consisting of four shafts in a square formAtion with pairs of bevel gears at the corners, two of the shafts (one of which 19" is shown) forming the top axes of the conveyors and the other two (of which one, 19"', is also shown~ carrying chain drives 19""
to the lower rolls of the pinch rolls 19l'.
At the bottom of the machine, before it passes under a guide roll 22 and onto the side walls of the expansion enclosure, each paper web is folded at each side by two-part guides 20 of per se known kind to form an edge lap 21 at ; each edge 13 of the expansion-enclosure side walls, passing - over beads of a few mrn diameter (not seen~) formed on the edges of the walls. Fig. 3A shows the success;ve stages ~i) to ~iv) of ormation of a lap, from above (at the left of the Fig.) and in section with the guides 20 shown (at the right of the Fig.). To urther assist in maintaining the position of the paper and hence cause it when within the expansion enclosure to follow the curve of the walls, an inextensible pressure-sensitive adhesive tape 21' is fed onto the under face of the paper before the folding~ from reels 21" mounted on the rnachine frame, so as to lie adjacent to the bead after the folding. The tape passes with the paper under the rolls 22, and strengthens it for its transit thrQugh the machine.
In operation of the rnachine the take off speed of the Eoam is balanced against the rate of feed of reactants.
A slight excess pressure is ml~intained in the expansion enclosure, for example of a few centimetres of mercury, and a transducer 23 in the base of the feeder channel monitors this pressure contLnuously.

Fig, 5 sh~ws on a larger scale the curved shape of the expansion enclosure sides; rnatched to the expansion of the foam. The Fig. is, further, rnarked up with figures for height, elapsed time and % of final expansion reached at a g;ven level for a particular HR~':polyurethane foaming reaction, The dwell time in the rnain (diverging) part of the expansion enclosure is in this example approximately two minutes9 and the foam reaches approximately 90% o full expansion ~the expansion rate is substantially â 10 linear up to that polnt) at the exit from the diverging path provided by the enclosure, This level is rnarked D
on the Fig, Above this is shown r~rked E the point at which 100% expansion is reached, that ;s to say at which the cells break and the material begins to breathe, The lPvel F (about 1 further minute from D) is that at which the material becomes sufficiently strong to support tractive forces and the conveyor takes over. The ~foaming height' is therefore no more than 1-1~ metres.
The breathing takes place upwards through the open-cell material above, and an incidental but very signi~icant advan~age o~ the rnachine is that an extractor hood can very readily be provided over the top of the foam path to remove the gases breathed from the foam, where for exarnple toluene cliisocycmate (TDI) is the isocyanate used, to keep vaporlsed tol-uene diisocyanate levels surrounding the machine down to perrnitted levels without use of large volumes of extraction air. This is an important practical advantage, given the high cost o~ extraction equipment, Compared ~ith mould processes and with * high resilience ~l~7~

horizontal foaming the exposure of material potentially giving off such materials is very small, almost the whole of the reaction mass being enclosed and part of the TDI
given off reacting as it passes up the colu~m. Further of course the actual rate of production of TD~ fumes is low compared with that from high output horizontal machines.

FORMULATION AND OPERATING EXAMPLES

The following are detailed examples of formulations and operating conditions.
Example 1 The machine shown in Fig. 3 was used:
A. Dimensions ; Paper = 100 g/m kraft 1.78 metres wide Film = 45 micron polyethylene film 1.10 metres wide Feed channel and expansion enclosure volume, total to parallel section = 0.95 m Feed channel volume = 0.03 m Conveyor speed = 0.77 metres/minute Conveyor length = 4 metres Total chemical input = 37 kg/minute Chemical input less reaction loss of 8% = 34 kg/mlnute Finished ~oam density = 26 kg/m Area of cross-section of fi.nished block = 1.70 m2.

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B. Formulation (flexible polyether foam) Parts by weight Polyether polyol, 3500 molecular weight 48 hydroxyl no. 100 Water 3 3 Conventional silicone surfactant 1.1 Conventional amine catalyst - Dabco 33LV 0.35 Tin catalyst - Stannous octoate 0.26 Trichlorofluoromethane (Arcton 11~ 4.00 'r 10 Toluene diisocyanate (80 : 20 TDI) 43.5 ~Dabco and Arcton are trade marks) C General Conditions Temperature of reaction mixture = 20C.
Rise time for 100% expansion (box pour~ = 110 seconds.
15 ` Chemicals mixed continuously in multi-component mix head with rotary mixer (3500 rpm). Air injected at rate of 1000 ml/minute for nucleation of foam.
Reaction mixture passed to the feed channel by two flexible plastics hoses 18mm internal diameter.
Pressure of the reaction mixture monitored by pressure sensor mounted in the bottom-centre of the feed channel.
Observed pressure during continuous running a 10 15 tnlTI/Hg .
D. Fxarnillation of foam blocks Block dimensions: 1.65 x 1~03 x 2.0 metres Trim loss - ~11 four skins removed = 4% by weight Block cross-section was rectangular Trimmed piece density = 26 kg/m Density variation - maximum density = 26.8 kg/m3 minimum density = 25.7 kg/m3 . -24-I.L.D. (indentation load deflection) hardness (203 mm diameter indentor, 460 x 460 x 75 mm sample) 50V/o compression Mean hardness - 22.5 kg Maximum hardness = 23.0 kg Minimum hardness = 22.0 kg Hot compression set = 4.5%
Tensile strength = 130 KPa Elongation at break = 230%
The above shows production of a foam of good properties in all respects.

The machine was set up generally in the same manner as in Example 1.
A Formulation Parts by wei~
Polyether polyol, 3500 molecular weight 48 hydroxyl no. 100 Water 4,3 Silicone surfactant 0.9 Amine catalyst - Dabco 33LV : Nlax,'~Al ratio 3 : 1 by weight 0.2 - 0~35 Tin catalyst - stannous octoate 0.28 Trichlorofl.uorolnethane - Arcton 11 1.5 Toluene diisocyartate (80 : 20 TDI) 53.6 B General Conditions _ Conveyor speed = 0.93 metres/minute Total chemical input = 38.3 kg/minute ,'; Trade Mark Chemical input less reaction loss of 8~5% = 35,0 kg/min.
During the run the level of amine catalyst was varied between 0.2 and 0.35 parts per 100 parts of polyol. It was noted that at the higher level of catalyst (i.e~ faster expansion reaction) the block thickness reduced {"thickness" is the dimension across the top of the diverging section~.
Decreasing the amine catalyst level returned the block thickness to normal.
C. Product :2 Foam blocks of finished density 22 kg/m and of good properties in all respects when tested as in Example 1 were given.

A high-resilience foam formulation based on an ethylene oxide "tipped" polyol of molecular weight 6000 and a proprietary lsocyanate - Desmodu~;MT58 from Bayer Chemicals ; Ltd, was run on the same machine as Examples 1 and 2.
Foam density = 36 kg/m Chemical input rate (net) - 35 kg/minute Conveyor speed = 0.55 metres/minute Again, good quality foam was produced.

DENSITY PROFII,ES
_ ___ . __ General].y, foam produced by the method of the invention shows propert;es comparable to conventionally produced foam. In respect oE symmetry of propert,y variation in the block however the foam produced is superior, as Figs. 6A to 6E show. (The diagrams give % variation about mean density, * Trade Mark ~7~

with mean dens;ty (A) and trim loss figures (B) alongslde.) All diagrams are after skin trimming. The prior foams of Figs. 6A to 6D all show a ~-ariation of properties broadly syr~netrical about the vertical centre llne, though w;th some variations where conditions at the two sides have not `~ been quite the sarne. Properties through the block from top to bottom however show considerable variation, undesirable in principle and noticeable in use when converted to large articles, such as mattresses~ especially if cutting is vertically rather than hori~ontally of the bloc~. In contrast the propertiès of blocks produced by the method of the invention are substantially symmetrical about the block centre, as shown in Fig. 6E for the density of the foam blocks of Example 1.

_ALCULATIONS

In considering the detail of control of the foaming, with reference in particular to Example 1, reference may be made to Fig. 7, showing the volume contained by the feed zone, expansion enclosure and take off path of the machine of Fig. 3 at various heights above the base of the feed chalmel, and Fig. 8, showing the foam expans-lon rise profile for a box pour of the formulation oE Example 1.
In Fig. 7 the curnulative volume is plotted vertically and the height above the base horiæontally. Perpend;cular A
is dropped at the height of the start of the parallel take off path, perpendicular B at the height of the start of the pinned conveyor. In Fig. 8 the percentage expanslon ~7gii~
. -27-is plotted vertically and the rise time in seconds (t) horizontally. Perpendiculars are dropped corresponding to an expansion of 10~/~, 20% etc. to 100%.
These plots are used to calculate the oam vol.ume at any interval, based on theory as follows.
Let Tloo be the time in seconds at wh;ch 100%
expansion is reached, D be the final foam density in kg/m , and W be the net foam input (total reactant input less reactant loss) in kg/min, and consider a time interval tl-t2 seconds, then, ignoring volume of original unexpanded poiymer:
:
Area under curve between tl and t2 t2 = ~ E x t ~
tl Now weight of foam dispensed in this time = w = 2 W x t kg _ ~ 60 tl Volume of foam represented by this weight t2 = V - ~ D x 100 t Substituting ~ and ~ into ~

Area under _ rve x W
t 6000 x D

The procedure is thus:

l. Plot rise curve - % expansion v. time in seconds.
2. Divide into vertical columns A, B ........ J corresponding to 10/o~ 20% .... r 100%~
3. Measure area of each column ~mcler curve.
4. Calculate volu~e of foam corresponding to each column A, B ...... J using formula V _ _rea under curve x W
6000 x D

5. From known reaction volume (volume of feed zone and expansion enclosure) relate to expansion height `:

- lO The actual calculations for Example 1 are:

i A - ~olume of partially expanded foam corresponding to time period of 110 seconds (100% rise time) TABLE I
Max. % ~ime Area under Calculated C~nulative Foam ex~ansion (seconds) rise curve foam volume volume h (m ) (m ) 19 60 0.013 0.013 0.1 165 0.036 0.049 0.25 250 0.05~ 0.103 0.40 49 315 0.069 0.172 0.50 57 360 0.078 0.250 0.60 66 ~95 0.108 0.358 0.69 585 Q.127 0.485 0.76 84 675 0.147 0.632 0.86 93 765 0.167 0.799 0.96 100 110 1615 0.352 1.151 1.15 ~ ~'7 Reaction volume up to parallel section = 0.95 m Height up to parallel section = 1.05 m i.e. foam reached 100% expansion at a point Ool m above start of parallel sec-tion.
B - Calculation of conveyor velocity:
___ Net chernical input rate must match foam output rate on weight basis.
If : fina7 foam density = D kg/m net chemical input = W kg/minute area of cross section of foam = A m Then : conveyor velocity = W
D x A
= 34 = 0.77 metres/minute.
26 x 1.7 C - Theory of expansion control Assume that velocity of conveyor is set for correct final density and throughput rate.
Consider each of three cases:
1. ~
All expansion occurs by end of diverging section.
Cell orientation maximised in hori~ontal direction.
Density correct.
2. T~oo too low _ . _ __ Foam will not make up to full width, the end of the diverging section not having been reached. Density will be higher. I-ligher pressure in expansion enclosure.

100 to~
~ .
Foam makes up to full width. Some expansion occurs ~7~

in parallel section. Cell orientation more isotropic.
Pin grip reduced since foam now takes longer to develop strength.
In practice it is arranged for the Tloo time to be marginally higher than theoretically required so as to ensure complete filling out.

SUMMARY OF ADVANTAGES
.

The advantages of the production of foam as described and discussed above are we believe clear. In summary they are:
- reduction of capital cost and space requirement for machines;
- convenient production rate wi-th smaller, continuously occupied labour force and less attendance required on machine in any case;
- reduction of storage and curing space required for product prior to further handling;
- lower rate and absolute amount of fume emission, giving ready and inexpensive compliance with statutory requirements;
- reduced start up and shut down waste, and similarly in grade and colour changes, owing to the lower rate of operation;
- no leathery top skin except at start up and thinner skins generally;
- symmetr:ical distribution of physical properties in the block;
- accurately controlled cross section~

.

~7~

All these rnatters add up to a major advance in foam production, allowing foam to be widely and economically made in moderate si~ed units serving individual rnarkets where neither capital for major installations nor transport for their products over large areas are availableO

Claims (28)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of continuous production of foamed material, wherein foam forming materials are fed from below at a control-led rate and the foamed material formed is drawn away from above at a corresponding rate, wherein foaming takes place in a diverging expansion enclosure bounded by moving sheet material constrained to follow a diverging path and drawn away from above so as to travel with the foaming material at a rate correspond-ing to its rate of travel, and wherein the enclosure is defined above by foam already expanded, at the sides by said sheet material, and below by a feed zone sealed to contain the foam forming materials, the enclosure leading into an upwardly directed take off path for the foam.

2. A method according to claim 1, wherein foaming commences in the feed zone and is completed in the expansion enclosure, contact with the travelling surfaces thus being made at an intermediate stage of reaction.

3. A method according to claim 1, wherein the travel-ling surfaces are constituted by webs of sheet material drawn over the walls of the expansion enclosure.

4. A method according to claim 3, wherein the webs pass up the take off path with the foamed material.

5. A method according to any of claims 1 to 3, wherein spiked conveyors are provided at one or more positions at the sides of the take off path, engaging the foamed material.

6. A method according to any of claims 1 to 3, wherein a pressure monitor is provided in the feed zone or in the expansion enclosure in contact with still-liquid foaming materials.

7. A method according to claim 1, wherein the expansion enclosure is generally wedge shaped, defined by a pair of parallel opposed walls and a pair of opposed diverging walls lying between the parallel walls, the feed zone being a channel at the lower edges of the diverging walls.

8. A method according to claim 7, wherein the diverging walls are shaped to match the enclosure to the expansion curve of the foaming materials.

9. A method according to claims 7 or 8, wherein the web at the parallel walls is a polyethylene or other plastics film passing up the take off path to be perforated by a spiked conveyor for the foam.

10. A method according to claim 7 wherein the web at the diverging walls is a paper web the edges of which are folded to lap round the edges of the walls onto the back at each side.

11. A method according to claim 10, wherein an inextensible pressure-sensitive tape is applied to each lap.

12. A method according to claim 11, wherein the diverging walls have edge beads at the sides away from the expansion enclosure, over which the paper laps are made and adjacent to which the tapes are applied.

13. A method according to claims 7 or 8 wherein, in the expansion enclosure, the separation of the parallel or the diverging walls or both is variable, with corresponding move-ment of the walls of the take off path, to allow variation in block width, in particular by pivoting or flexing the diverging walls.

14. A method according to any of claims 1 to 3, wherein the expansion enclosure and take off path are circular in cross section for the production of cylindrical blocks for peeling.

15. A machine for continuous production of foamed material, comprising feed means for feeding foam forming materials from below at a controlled rate, take off means for drawing the foamed material formed away from above at a corresponding rate, means forming a diverging expansion enclosure bounded by moving sheet material constrained to follow a diverainq path and drawn away from above so as to travel with the foaming material at a rate corresponding to its rate of travel, in which diverging ex-pansion enclosure foaming takes place, wherein the enclosure is defined above by foam already expanded, at the sides by said sheet material, and below by a feed zone sealed to contain the foam forming materials, the enclosure leading into an upwardly directed take off path for the foam.

16. A machine according to claim 15, so dimensioned that foaming commences in the feed zone (11) and is completed in the expansion enclosure (1), contact with the travelling surfaces (15, 17) thus being made at an intermediate stage of reaction.

17. A machine according to claim 15, wherein means (3, 19') are provided to draw webs of sheet material (15, 17) over the walls (13, 14) of the expansion enclosure (1) to constitute the travelling surfaces.

18. A machine according to claim 17, wherein said means (3, 19') pass the webs (15, 17) up the take off path with the foamed material (8).

19. A machine according to any of claims 15 to 17, wherein spiked conveyors (3) are provided at one or more positions at the sides of the take off path, to engage the foamed material (8).

20. A machine according to any of claims 15 to 17, wherein a pressure monitor (23) is provided in the feed zone (11) or in the expansion enclosure (1) at a position to contact still-liquid foaming materials.

21. A machine according to claim 15, wherein the expansion enclosure (1) is generally wedge shaped, defined by a pair of parallel opposed walls (14) and a pair of opposed diverging walls (13) lying between the parallel walls (14), the feed zone being a channel (11) at the lower edges of the diverging walls.

22. A machine according to claim 21, wherein the diverging walls (13) are shaped to match the enclosure to the expansion curve of the material to be foamed in the machine.

23. A machine according to claims 21 or 22, wherein the web at the parallel walls (14) is a polyethylene or other plastics film (15) passing up the take off path to be perforated by a spiked conveyor (3) for the foam (8).

24. A machine according to claim 21, wherein the web at the diverging walls (13) is a paper web (17) the edges of which are folded to lap (21) round the edges of the walls (13) onto the back at each side.

25. A machine according to claim 24, wherein an inextensible pressure-sensitive tape is applied to each lap (21).

26. A machine according to claim 25, wherein the diverging walls have edge beads at the sides away from the expansion enclosure (1), over which the paper laps (21) are made and adjacent to which the tapes are applied.

27. A machine according to claims 21 or 26, wherein, in the expansion enclosure (1), the separation of the parallel (14) or the diverging (13) walls or both is variable, with corresponding movement of the walls (2,3) of the take off path, to allow variation in block width, in particular by pivoting or flexing the diverginig walls (13).

28. A machine according to any of claims 15 to 17, wherein the expansion enclosure and take off path are circular in cross section for the production of cylindrical blocks for peeling.