Title: Method of and means for producing a body of a foamed solid.

Technical Field:

A first aspect of the present invention relates to a method of producing a body of foam and is especially useful in the production of a pad of foamed solid material such as are commonly used for pads when packing articles in containers. A second aspect of the invention relates to means for producing a pad comprising a body of foamed solid ma erial.

Background Art:

Hitherto a wide variety of packaging materials have 0 been used to constitute pads between an article and a container for the article. These known materials include wood shavings, paper strips, cardboard and pads of foamed solid materials. All of these materials are bulky and hence require the provision of a large volume for storage.

5 Foamed solid materials which have commonly been used for pads in packaging are produced from polymerisable monomers or resins by causing polymerisation to be accompanied by the generation of vapour or gas in the composition. Foamed solid materials Λvhich have been produced in this way 0 include foamed polystyrene and foamed polyurethanes . For foaming the compositions, there have been used volatile liquids which vapourise when they absorb the heat of re¬ action released during polymerisation and water which reacts with isocyanates to produce carbon dioxide. To produce

- ^~ pads of foamed solid material of predetermined shape, the polymerisation and foaming are carried out in a mould which

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is used for the production of successive pads.

Summary of the Invention:

According to a first aspect of the invention, there is provided a method of producing a body of foamed solid comprising the steps of preparing a pack comprising first and second foam producing constituents, the pack having means for normally maintaining the constituents in isolatio and performing an operation on the pack to mix the constit¬ uents together to cause them to react to produce foam w ^r ith the pack.

According to the invention there is also provided a method of producing a pad wherein there are sealed within a flexible envelope a plurality of foam producing constitu¬ ents, at least one of said constituents being polymerisable said constituents are maintained separate from one another for a period of time, the constituents are then mixed and interact to produce a foam within the sealed envelope, the foam expands the envelope and the foam sets whilst i the sealed envelope.

According to a further aspect of the invention there is provided a pack comprising foam producing constituents in respective separate compartments within a flexible, sealed envelope which can, whilst remaining sealed, enclose a volume which is a plurality of times greater than the aggregate volume of said constituents, at least one of sai constituents being polymerisable in the presence of the other constituents and the pack being adapted to permit, when required, mixing of said constituents to produce a polymeric foam in the envelope.

Prior to mixing of the constituents within the pack, the envelope can be maintained in a compact configuration

so that the pack occupies only a relatively small volume. This facilitates transport and storage of the pack. Vhen the pad is required, the constituents can be allowed to interact to produce the pad, the size and shape of which may be determined by the envelope. Alternatively, the envelope may be confined between an article and a container so that the shape of the pad is partly determined by the article. Contamination of equipment, personnel or the article is avoided because the envelope remains sealed.

Various materials which will interact to produce a foamed solid may be used in the pack. The interaction between the constituents may involve polymerisation by straight chain extension or cross linking of polymeric chains. The polymerisable constituent may be a monomer, a mixture of monomers or a resin. Prior to mixing of the constituents in the pack, the polymerisable constituent is in liquid form so that it can be foamed. Ivhen the constituent is polymerised, the foam sets.

Brief Description of the Drawing: One example of a pack embodying the invention will now be described with reference to the accompanying drawing which shows diagrammatically an elevation of the pack.

Detailed Description:

The pack shown in the drawing comprises an outer, sealed envelope 10 of flexible translucent plastics sheet materialβ The sheet material may be polythene or a poly¬ carbonate and may have a gauge of 250, that is a thickness of 0.0025 inch, approximately 6k micron.

¥ithin the outer envelope 10 there is provided a container 11 made of similar flexible sheet material, al¬ though the material of which the container 11 is -formed may have a gauge different from that of which the outer envelope 10 is formed. The container 11 is made from a tube of the

sheet material and the walls of the tube are sealed together _. at the ends, as shown at 12 and 13• The walls are also sealed together intermediate the ends as shown at Ik . The seal 13 is arranged to be a permanent seal whilst the seal Ik is arranged to be semi-permanent and relatively easily rupturable by establishing pressure in one of the compartments 1 and 16 which are separated by the seal Ik . The end seal 12 is also a semi-permanent seal but is more difficult to rupture than is the seal Ik .

Within the compartments 15 and lβ are provided two different foam-producing constituents which are capable of interacting to produce a foamed solid. These constitu¬ ents may be materials known for use in the prepation of foamed solid bodies. At least one of the constituents is polymerisable. Typically, the compartment l6 contains a constituent comprising a polyol and the compartment 15 contains a constituent comprising a polyisocyanate . The constituent in the compartment 16 may further comprise a small quantity of water. Alternatively, one of the constituents may comprise a volatile liquid, for example a freon or arcton. The relative proportions of the constituents depends upon the nature of the final pad required and may be 1 : 1 or : - _~ . The constituent • in each of the compartments is in liquid form.

^" When it is desired to use the pack to make a packagin pad, the pack is taken and there is applied to one of the compartments 15 and 16 a pressure which is sufficient to cause the seal Ik to rupture. Pressure is then applied alternately to the compartments 15 and iβ to cause the constituents therein to mix together. When they are mixed, the constituents interact to produce a polyurethane foam. The polyol and polyisocyanate polymerise together. If water is present, this reacts with some of the polyiso¬ cyanate to produce carbon dioxide which causes the mixture

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to foam. In a case where a volatile liquid is present, the heat released by the polymerisation reaction causes vapour to be produced from the liquid and this vapour causes the mixture to foam. To stabilise the foam and to control the cell size, there may be included in one or other of the constituents a surfactant. The volume of foam produced by interaction between the constituents in the compartments 15 and 16 greatly exceeds the aggregate volume of these compartments. Accordingly, the foam causes the seal 12 to rupture and the foam escapes into the envelope 10 from the compartments 15 and 16. The foam causes the envelope 10 to expand to enclose a volume which is a plurality of times greater than the aggregate volume of the compartments 1 and lβ.

If desired, the pack may be placed in a box or other container before the foam sets, either before foaming occurs or during foaming, so that there is produced a body of foamed polyurethane which has a shape determined, at least in part, by that of the container. Alternatively, "the shape of the body of foamed polyurethane may be deter¬ mined by the shape of the envelope 10. The form of the envelope may be varied according to the required shape of tie body of foamed polyurethane.

If required, the container 11 may be omitted and a suitable division formed in the outer envelope 10 itself to separate the consituents from each other. Such division may be formed by twisting the envelope, by forming a fold transversely across the envelope and securing the fold with a clip or by forming a semi-permanent seal, such as a heat seal, between the walls of the outer envelope intermediate its ends.

In a further alternative arrangement, integral inner and outer envelopes are formed from a single piece of

flexible tube by sealing the walls of the tube together to provide two compartments with a semi-permanent seal between them and with a further semi-permanent but strong seal between the compartments and the remainder of the envelope. Wit this arrangement, the constituents could again be mixed together by rupturing the intermediate sea and applying pressure alternately to the compartments to cause the liquids to mix before foaming occurs to a degre sufficient to cause the rupture of the stronger semi- permanent seal, following which the foam would expand int and fill the remainder of the envelope.

It is preferred that the constituents occupy their respective compartments substantially completely and are separated by a rupturable seal, so that the constituents can be thoroughly mixed before any significant foaming occurs. This avoids the escape of unmixed constituent in the outer envelope and the possibility of unmixed constit ent being present in the body of foamed solid. The prese of unmixed constituent in the body of foamed solid may be disadvantageous, in the event of inadvertent rupture of t outer envelope.

As is well known, the density and other properties of the body of foamed solid can be adjusted by appropriate selection of the constituents.

Various constituents may be used to produce the foam For example, one constituent may comprise a phenolic base polyol, the other constituent comprising a catalyst for causing polymerisation of the polyol. In this case, one of the constituents may comprise a volatile liquid from which a vapour is produced by the heat of reaction releas during polymerisation of the polyol. There may be used systems comprising three or more constituents which are maintained in isolation until foaming is required and the

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mixed together. A number of compartments appropriate to the number of constituents would be provided, these compartments being separated by rupturable seals so that the constituents can be mixed when required.

It w ^r ill also be appreciated that the invention may be used to form foamed pads of any desired shape for uses other than packaging, for example for insulation against temperature change, noise and vibration. The invention may also be used to provide permanent, semi-permanent or emergency buoyancy.

In a case where one of the constituents comprises an isocyanate or other toxic substance, it is preferred that this constituent is contained in a compartment separated from a further, less toxic constituent by a semi-permanent seal and the compartment containing the toxic constituent having a further semi-permanent seal, stronger than the seal between the compartments, through which the mixed constituents can escape into the outer envelope. With this arrangement the toxic constituent is swept from its compartment by the expanding mixture and the risk of any of the toxic constituent remaining unreacted when the foam has set is reduced. It will be understood that all of the constituents remain sealed in the outer envelope and only in the event of accidental rupture of the outer envelope could the presence of unreacted toxic constituent in the foam be harmful. Normally, the invention avoids contamination by any of the constituents or by the foam of personnel, apparatus and any articles associated with the foam.

The preferred way of forming the semi-permanent seals is to heat seal the plastics sheet material by applying heat thereto for a period which is shorter than the minimum period necessary to form a proper \reld of the sheet material. Usually, when forming a proper weld,

the sheet material is heated sufficiently to soften or fuse the material throughout its thickness at the site of the weld. It is believed that by heating the sheet material for a shorter period, the sheet material is not softened or fused throughout its entire thick¬ ness. I have found that the semi-permanent seals can be formed in this way conveniently by using for the container 11 sheet material which is thicker than that used for the outer envelope 10. Typically, the sheet material used for the container 11 has a thickness of 0.005 to 0.0075 inch, that is approximately 130 micron to approximately 200 micron.

The container 11 shown in the accompanying drawing is formed from a length of tube and the compartments 15 and l6 occupy successive parts of the length of the tube. Alternatively, the container may be formed from a length of tube by providing a semi-permanent seal extending along the length „of the tube, so that the two compartments lie side-by-side and together occupy a common part of the length of the tube. There may be formed across both compartments at one end of this length of the tube a permanent seal and at the opposite end of the part of the tube either semi-permanent seals which close respective compartments, or a semi-permanent seal which closes one compartment and a permanent seal which closes the other compartment, or permanent seals which close respective compartments. In the latter case, the container would be ruptured by the expanding foam but not necessarily at a seal.

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