A PROCESS FOR COATING FOAM

Abstract: This invention relates to a process for sealing any foamed rubber product or foamed plastic product having a foam cell structure, excluding foamed polystyrene, to provide a continuous, flexible, impervious surface including applying to the surface a primer which penetrates partially into the foam cell and then applying a polymeric composition to the primer-treated surface. The invention also relates to formulations used in the process and products produced by the process.

Description: A PROCESS FOR COATING FOAM FIELD OF INVENTION This invention relates to foams, such as foamed plastics and foamed rubber. In particular, this invention relates to process and formulations for sealing foam products. BACKGROUND TO THE INVENTION Foamed plastics are porous, very light substances made of various plastics such as epoxide resins, urea resins, polyurethane, polystyrene, polyethylene or polyvinylchloride. Phenolics, silicones and cellulose acetates can also be foamed. In fact, under the right conditions, almost any thermosetting or thermoplastic resin can be converted into a foam. Foamed plastics have a cellular structure and can be divided into foams having a closed cell structure and foams having an open cell structure. Foams which have a closed cell structure are synthesised by incorporating a blowing agent or a propellant into the plastic which either evaporates or decomposes at the fusion point of the plastic, releasing gas bubbles which are trapped during the gelling of the plastic. Foams which have an open cell structure are synthesised by incorporating an inert gas into the resin under pressure and then releasing the mixture to the atmosphere and curing the resulting foam. Foams may either be flexible or rigid and have a wide variety of uses. Rigid or hard foams such as polyethylene are particularly used for thermal insulation, or furniture and building panels, whereas softer foams are used for cushioning materials, all types of padding and sponges. Foamed rubber is a highly elastic, porous and lightweight rubber. It is made by various methods using natural or synthetic latex which is mixed with various ingredients and converted to foam. The foam rubber can also be moulded and vulcanised. Foam rubber contains approximately 85% air and, similar to foamed plastics, can be used for a wide range of consumer goods including padding for furniture, mattresses and pillows. Inherent in the majority of uses of foamed plastic or rubber (foam) is the fact that the foam is generally required to be covered or sealed in some way, for both functional, hygienic as well as aesthetic reasons. The covering and sealing of foam mattresses, pillows, cushions and similar products inhibits the build-up of dust and dust mites in such products. This has significant health benefits. The covering and sealing of such foam products is particularly important in the medical industry where foam is used for mattresses, pillows, cushions, commodes and operating theatre aids, with plastic or some other covering material, purchased and stitched or made up to cover the foam for the mattresses etc. There have been increasing instances of hospital patients catching infections from such foam mattresses, pillows and cushions, due to the fact that the infection had harboured in either the stitched seams of the covering or had actually lodged in the foam itself. In order to reduce the sites on the covering or foam where the bacteria can be deposited, and to prevent such problems of infection, manufacturers have attempted to provide a plastic coating which will adhere to foam and thus completely seal it. One US manufacturer has attempted to coat foam by dipping the foam in a vat of coating. However, the method is not able to be used on open cell foams, and further, the coating has a tendency to delaminate from the foam. Various lamination methods have also been tried to clinically seal foam products. For example, GB patent 1 588 941 discloses the sealing of a pad of foam material by a plurality of spray coatings of a flexible-non porous material such as polyvinylchloride (PVC), at least the final coating of which must contain electrically conductive carbon particles. However, these methods have either resulted in no bonding of the laminate to the foam, or a slight initial bonding which later delaminated when the total foam was sealed, resulting in the plastic laminate cover falling off the foam. OBJECTS OF THE INVENTION Thus, one object of this invention is therefore to provide a process for sealing foam products such that a continuous, seam free, sealed surface is obtained; and with the foam still maintaining its flexibility and its foam-like characteristics. Another object of this invention is to provide a flexible foam product with a continuous, seam free, sealed surface. STATEMENT OF INVENTION Accordingly, a first aspect of the invention provides a process of sealing any foamed rubber product or foamed plastic product having a foam cell structure, excluding foamed polystyrene, to provide a continuous, flexible, impervious surface, said process including: (i) applying to a surface of said foamed product a primer of foam-penetrating viscosity, such that the primer penetrates partially into the foam cell structure at least partially coating said surface, and (ii) applying a first polymeric composition onto the primer-treated surface, and, optionally, (iii) applying at least one additional layer of a second polymeric composition to the treated surface. Preferably, the first polymeric composition, in association with the primer, forms a sealed layer onto which the at least one layer of second polymeric composition may be applied. A second aspect of the invention provides a foamed product having a continuous, flexible, impervious sealed surface which has been produced according to the above process. A third aspect of the invention provides a sealed foamed plastic or foamed rubber product — excluding foamed polystyrene products — having surfaces at least partially coated with a primer and at least one layer of a polymeric composition such that at least a majority of foam cells in the foamed product are sealed. Preferably, the surfaces of the product are substantially, or, preferably, completely coated with the primer and polymeric composition. A fourth aspect of this invention provides a formulation, when used as a primer and/or as a polymeric composition in the process described herein, said formulation including an adhesive polymeric resin. The crux of this invention lies in the fact that the process of sealing is integral or inherent with the foam structure itself. Thus, the sealing does not form a separate skin on top of the foam which can be lifted off the foam, but instead the sealing occurs at least partially within the foam cell structure below the surface of the foam. This is due to the fact that the primer is understood to form a mechanical bond with the foam within the foam cell structure and the subsequent application(s) of polymeric composition(s) is understood to result in a chemical bond with the primer and build up the sealing membrane film so that the foam is substantially impervious to liquids. The final foam product has a sealing elastomeric membrane which is inherent with the foam structure itself and cannot be separated from the foam. Advantageously, the sealed foam still retains its flexibility and its other general foam characteristics, yet is substantially impervious to liquids and infectious agents such as bacteria. Further, the sealed foam can be autoclaved and cleaned with standard antibacterial and antifungal agents, without jeopardising the imperviousness of the sealed layer. Preferably, the foamed rubber or plastic is foamed polyurethane or polyethylene — most preferably, polyurethane foam. Also, preferably, the primer includes any adhesive polymeric resin including both monomer and co-polymer resins. More preferably, the primer includes at least one of the following: chlorinated rubber, rubber based polymeric resins and their derivatives including synthetics, elastomeric polyurethane, elastomeric acrylics and their derivatives including styrene acrylic, silicone and siiicone derived resins and vinyl resins. Still more preferably, the primer includes a co-polymerised polyvinylchloride (PVC) composition. Most preferably, the primer includes a polyvinyl chloride/poly vinyl acetate copolymer. Preferably, the primer is fast drying such that it penetrates into the foam and dries before it passes through the foam. More preferably, the primer is applied to the foam such that it penetrates the foam to a depth of at least 1mm below the foam surface before it dries. Most preferably, the primer is applied to the foam such that it penetrates the foam to a depth of no more than 2 to 4mm below the foam surface before it dries. Preferably, the first polymeric composition includes any adhesive polymeric resin including both monomer and co-polymer resins. More preferably, the first polymeric composition includes at least one of the following: chlorinated rubber, rubber based polymeric resins and their derivatives- including synthetics, elastomeric polyurethane, elastomeric acrylics and their derivatives including styrene acrylic, silicone and silicone derived resins and vinyl resins. Still more preferably, the first polymeric composition includes a co- polymerised polyvinylchloride (PVC) composition. Most preferably, the first polymeric composition includes a polyvinyl chloride/poly vinyl acetate copolymer. Equally most preferably, the first polymeric composition includes the same adhesive polymeric resin as is included in the primer. Preferably, the first polymeric composition is applied by being forcefully sprayed under pressure or blasted into the foam structure. Preferably, the second polymeric composition which is applied includes any adhesive polymeric resin including both monomer and co-polymer resins. More preferably, the second polymeric composition includes at least one of the following: chlorinated rubber, rubber based polymeric resins and their derivatives- including synthetics, elastomeric polyurethane, elastomeric acrylics and their derivatives including styrene acrylic, silicone and silicone derived resins and vinyl resins. Still more preferably, the second polymeric composition includes a co- polymerised polyvinylchloride (PVC) composition. Most preferably, the second polymeric composition includes a polyvinyl chloride/poly vinyl acetate copolymer. Also most preferably, the second polymeric composition includes the same adhesive polymeric resin as the first polymeric composition. Equally most preferably, the second polymeric composition includes the same adhesive polymeric resin as the primer which is initially applied to the foam. Preferably, the additional layers of the second polymeric composition are applied sequentially by a coat on coat process of application. Finally preferably, the sealing coat is built up to a thickness of at least 450 to 650 microns. This invention is of such a breakthrough nature that the applications of the foam-sealing process are endless. Such areas of application will include, but will not be limited to: a) the health industry for cushions, seats, mattresses, flotation products, furniture and equipment, b) the marine industry for cushions, matting and protective covers including buffers, c) the sports industry for matting, pole surrounds and cushioning in general, d) the domestic industry for matting, mattresses, flotation equipment, cushions and underlays. e) the hospitality industry for cushions, flotation products, furniture and equipment, and f) the motor industry for cushions, underlays and overlays, thermal and acoustic insulation, g) any fabric product capable of covering foam (such as cotton, canvas and synthetic fabrics; and h) industry generally where foams are used. DETAILED DESCRIPTION OF THE INVENTION Foamed Plastic/Rubber Any foamed rubber product or foamed plastic product having any standard irregular foam cell structure — whether it be open cell or closed cell — can be sealed according to the process of this invention — except for polystyrene. Polystyrene is not receptive to any of the polymeric resins which can be used in the primer or in the coating compositions. The solvents in the polymeric compositions and primer in fact dissolve the polystyrene structure. While a styrene based acrylic resin could be used to seal polystyrene, the sealed foam product which results will not be flexible, but will instead be rigid. A rigid sealed foam product is generally not desirable. Primer The primer is required to have a viscosity which is 'thin' enough such that upon contact of the primer with the foam, it can immediately penetrate through the foam surface and permeate into the foam cell structure. This is sometimes termed 'water thin', as the primer is effectively as thin as water. The primer is also preferred to be fast drying. 'Fast drying' effectively means that the primer must dry before it penetrates more than a few millimetres below the foam surface into the foam cell structure. The polymeric resins which are preferred as primers for this invention all dry within seconds of contacting and beginning to permeate through the foam cellular structure. Of course, if the primer composition is somewhat more viscous and takes some time to penetrate past the foam surface into the foam cellular structure, then it will not need to be so fast drying. The primer can be any adhesive polymeric resin. The resin is of course incorporated with the usual acceptable excipients including solvents into the primer formulation which is applied to the foam surface. A person skilled in the art of polymeric resins would easily be able to determine an appropriate primer formulation for application in this invention. Most effectively, the primer is applied to the foam by spraying onto the foam surface. The primer penetrates the foam cell structure and slides down the inside of the cell walls of the foam cells present in the cellular structure. As the primer dries, it forms a layer on the inner surfaces of the foam cell walls it has contacted. All the cells in the foam have preferably been at least partially coated with the primer. Preferably the primer has penetrated and coated all the foam cell walls to a depth no more than about 2 to 4mm below the foam surface. The primer coating is not necessarily consistent from one foam cell to another. For example, one foam cell may have an internal circumferential primer coat which exists between 1-2mm below the foam surface, whereas another foam cell may have its internal walls primer coated right from the foam surface to about 3 to 4mm below the surface. Further the primer layer may be of varying thickness within a cell or from one cell to another. However, the primer coating is such that the foam cells remain 'cells' insofar as the coat does not form a seal or a 'plug' which blocks the central space of the cell. In summary, effectively, the primer forms a mechanical bond with the foam cell structure. First polymeric composition The first polymeric composition is required to be applied 'into' the surface of the foam. This means that it is applied onto the surface of the foam but is so forcefully applied such that it at least penetrates just below the surface of the foam. The most preferred method of application is a pressurised spray gun. The application of the first polymeric composition can occur any time after the application of the primer. In fact the primer can still be wet or it can be dry. The first polymeric composition includes an adhesive resin which is most preferably identical to, or of the same family as the resin which is applied as the primer. The first polymeric composition thus forms a chemical bond with the primer to form a seal which is effectively like a film or membrane. This application generally seals the majority of the foam cells. Of course the extent of the sealing is dependent on a number of factors, including the thickness of the resin used in the polymeric coating. It is possible that only one application of the first polymeric composition may be sufficient to create a sealing layer which is substantially impervious to liquids and is of at least 450 to 650 microns thick. However, while the application of the first polymeric composition generally results in the majority of foam cells being filled or webbed over such that a seal is formed, it is most preferable to apply further coats as described below, particularly if the blasting of the first polymeric composition into the foam surface has not resulted in total sealing, to build up a sealing coat. The sealing coat is in the form of an elastomeric membrane due to the usage of an adhesive resin. Second polymeric composition While after the application of the first polymeric composition into the foam surface, a seal has generally formed, it is possible that either the seal is somewhat fragile, or in an exceptional case, is not complete. It is then preferable to sequentially apply one or more further coats of a second polymeric membrane onto the surface of the sealed foam structure. This application can occur at any time after the application of the first polymeric composition. The subsequent applications can occur by use of a spray gun, painting, dipping or other appropriate methods. Further, it is most preferred that this second polymeric composition is the same as or includes the same polymeric resin as the first polymeric composition. In this way, a seal is built up which preferably consists of primer, first polymeric and second polymeric compositions which are all identical or which all include an identical adhesive resin. 450 microns is the preferred minimum thickness of the membrane seal built up by the coat on coat application of the second polymeric composition. This application is preferably by means of a spray. An adhesive resin is of course incorporated with the usual acceptable excipients including solvents into the first and second polymeric compositions which are applied. A person skilled in the art of polymeric resins would easily be able to determine the appropriate polymeric compositions for application in this invention. A preferred embodiment of the process according to the invention will now be described. A piece of flexible polyurethane foam of any thickness and size is taken. Any moisture or surface contamination (such as dirt, dust or grease) should be removed. The foam should then be placed in such a way that application can be executed readily from any angle. Polyvinylchloride/polyvinylacetate copolymer is then applied by spraying or painting the surface of the foam. This copolymer immediately permeates through the cellular structure of the foam and being a fast-drying adhesive, penetrates no more than about 3mm into the foam before it dries and adheres in the foam, forming a mechanical bond with the foam. At this thickness of around 3mm, the foam is not rigid and maintains its flexibility. Thus it can be used in all its usual foam applications. A pressure spray gun or any other high pressure external atomising equipment is filled, for convenience, with a polymeric composition containing the same copolymer. At any time after applying the primer, preferably at least 10 minutes later, the polymeric composition is blasted into the foam across its entire surface area. A good heavy layer of the polymeric composition should be applied to the primed area. Once a first total coat of pressure spray application has been achieved, the polymeric composition is built up into a membrane coat by a sequential coat on coat application of the composition onto the foam by either painting or dipping or, preferably, surface spraying in order to ensure that a very fine cobweb coating has been achieved over the entire surface of the coated area. To bridge small gaps or holes in the foam, the spray gun should be held 60-90cm (2-3 ft) from the surface of the foam. The trigger should be squeezed slowly until feathers or threads of the composition appear. These feathers will bridge across openings to produce a web on which a proper wet coat can be applied. This operation should be done with care so that the normal film build can be applied on top of the completed "webbing" process. The high build elastomeric membrane which is formed has the ability to bridge holes in the foam. Once the dry membrane coat is 450 microns thick, it is impervious to liquids and most gases. At 550 microns, the membrane is tensile with total elasticity. At 950 microns, the membrane is impervious to everything but Freon gas. Manufacture of Formulations The formulations suitable for use in the process of the present invention, are generally manufactured in a heat jacketed, medium speed closed mixing vessel. A multi-step process is usually performed in the manufacture of the formulations which can generally be described as follows: Step one - Pump in solvents according to formulation. Step two - Slowly add in resins while the mixer is on. Step three - Start heating the vessel to a maximum of 60°C over three hours. Step four - Add plasticisers and stabilizers during the heating process. Step five - Once the mix is up to specified temperature, allow it to continue stirring for one hour before adding any other component. This allows the components to fuse or bind together, and is called copolymerisation. Step six - SLOWLY add pigments and fillers which have been prepared as a premix. Step seven - Add all other additives and allow to continue stirring for one hour. The formulation should not be canned until it has cooled to ambient temperature. Examples Suitable examples of formulations suitable for use in the subject invention are given below. The numerals given in the third columns (below) correspond with the relevant process step at which the relevant components are added to the formulation during manufacture (as described above under the heading 'Manufacture of Formulations'). Example 1: A formulation which is particularly suitable for use as a primer is set out below. COM PONENTS (Kgs/100L) PROCESS STEP Toluol 17.000 Xylol 17.000 Methylisobutylketone 20.800 Acetone 4.700 Methylethylketone 16.000 Union Carbide VMCH 7.500 2 Union Carbide VAGH 7.500 2 PPrrooppyylleennee OOxxiiddee 00..444499 6 Example 2: Another formulation for use as a primer in the process of this invention is given below. COM PON ENTS (Kgs/100L) PROCESS STEP Toluol 17.00 Xylol 17.00 Methylisobutylketone 21.00 Acetone 4.70 Methylethylketone 16.00 Union Carbide VMCH 7.50 2 Union Carbide VAGH 7.50 2 Tri iso trimelitate 2.00 6 Propylene Oxide 0.45 6 Example 3: An example of a preferred polymeric composition for both the first and second polymeric compositions is given below. COM PONENTS (Kgs/100L) PROCESS STEP Acetone 26.360 1 Methylethylketone 26.360 1 Toluol 12.070 1 Methylisobutylketone 0.625 1 Union Carbide VYNS (90:10) 12.070 2 Union Carbide VYHH (86:14) 4.010 2 Union Carbide VMCH (86:13:1 ) 0.990 2 Cereclor AS52 Chlorinated Paraffin 2.250 4 Diisooctylphthalate 3.000 4 Trioctyltrimellitate 4.560 4 Dioctyladipate 1.430 4 Wetting agent 0.053 6 Titanium dioxide 0.850 6 Flamtard fire retardant 0.850 6 Calcium carbonate 0.850 6 Dibasic lead phosphate 5:2 0.562 6 Aluminium paste 1.020 6 Bentonite 0.925 6 20% Black pigment paste 0.001 6 Example 4: Another suitable formulation for use as a polymeric composition in the process is as follows. COMPONENTS (Kgs/100L) PROCESS STEP Toluol 16.75 1 Xylol 16.75 1 Methylisobutylketone 32.50 1 Union Carbide VYHH 14.50 2 Tri isotrimelitate 3.20 4 Dibasic lead phosphite 2.30 4 Tinuvin 1130 .70 4 Bisphenol A .32 4 Tiona 575 3.90 6 Alcolec S .32 6 Corflex 880 1.30 6 Methylisobutylketone 3.20 6 A particularly preferred primer is 'POLYERGIC Primer 200TM' ι which is a water clear, low viscosity, fast-drying primer. A particularly preferred polymeric composition is 'POLYERGICTM - membrane covering.

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A process of sealing a foamed rubber product or foamed plastic product having a foam cell structure, excluding foamed polystyrene products, to provide a continuous, flexible, impervious surface, said process including: (i) applying to a surface of said foamed product a primer of foam-penetrating viscosity, such that the primer penetrates partially into the foam cell structure at least partially coating said surface, and (ii) applying a first polymeric composition onto the primer-treated surface. 2. A process according to claim 1 , including the additional step of applying at least one additional layer of a second polymeric composition to the surface. 3. A process according to claim 1 or claim 2 wherein the first polymeric composition, in association with the primer, forms a sealed layer on the surface of the foamed product. 4. A process according to any one of claims 1 to 3 wherein the primer is applied such that it penetrates the foam cell structure to a depth of at least 1 mm below the surface. 5. A process according to claim 4 wherein the primer is applied to the foamed product such that it penetrates into the foam cell structure to a depth of between 2 to 4 mm below the surface. 6. A process according to any one of claims 1 to 5 wherein the primer is applied by painting or spraying the surface. 7. A process according to any one of claims 1 to 6 wherein the first polymeric composition is applied under pressure. 8. A process according to claim 7 where the first polymeric composition is applied by a pressurised spray gun or any other high pressure external atomising equipment. 9. A process according to any one of claims 2 to 8 wherein the second polymeric composition is applied by spraying or painting the surface. 10. A process according to any one of claims 2 to 9 wherein the first and second polymeric compositions are applied until substantially all of the foamed product is sealed. 11. A process according to any one of claims 1 to 10 wherein the primer, the first polymeric composition and the second polymeric composition include a formulation containing an adhesive polymeric resin. 12. A process according to claim 11 wherein the adhesive polymeric resin is a monomeric resin or a co-polymeric resin. 13. A process according to claim 11 or claim 12 wherein the adhesive polymeric resin includes one or more of chlorinated rubber, rubber based polymeric resins and their derivatives and synthetics, elastomeric polyurethane, elastomeric acrylics and their derivatives including styrene acrylic, silicone and silicone-derived resins and vinyl resins. 14. A process according to claim 13 wherein the adhesive polymeric resin includes a co-polymerised polyvinylchloride (PVC) composition. 15. A process according to claim 14 wherein the adhesive polymeric resin includes a polyvinylchloride/polyvinylacetate co-polymer. 16. A process according to any one of claims 11 to 15 wherein the viscosity of the primer is such that, upon contact with a surface of the foamed product, the primer is adapted to penetrate partially into the foam cell structure of the foamed product. 17. A process according to any one of claims 11 to 16 wherein the primer is adapted to dry after penetrating no more than about 4 mm below the surface. 18. A process according to any one of claims 1 to 17 wherein the formulations of the primer, the first polymeric composition and the second polymeric composition are the same or different. 19. A process according to claim 18 wherein the formulation of the primer, the first polymeric composition and the second polymeric composition are the same. 20. A formulation, when used as a primer, a first polymeric composition or a second polymeric composition in the process defined in any one of claims 1 to 19, wherein said formulation includes an adhesive polymeric resin. 21. A formulation according to claim 20 including an adhesive monomeric resin or an adhesive co-polymeric resin or both. 22. A formulation according to claim 20 or claim 21 including at least one of chlorinated rubber, rubber based polymeric resins and their derivatives and synthetics, elastomeric polyurethane, elastomeric acrylics and their derivatives including styrene acrylic, silicone and silicone derived resins and vinyl resins. 23. A formulation according to claim 22 including a co-polymerised polyvinylchloride (PVC) composition. 24. A formulation according to claim 23 including a polyvinylchloride/ polyvinylacytate co-polymer. 25. A formulation according to any one of claims 20 to 24, having a viscosity such that, upon contact with the foam, the formulation penetrates the foam cell structure to a depth of at least 1 mm below the surface. 26. A formulation according to claim 25 wherein the viscosity formulation is such that the formulation penetrates the foam cell structure to a depth of between 2 to 4 mm below the surface. 27. A process of sealing a foamed rubber product or foamed plastic product having a foam cell structure, excluding foamed polystyrene products, to provide a continuous, flexible, impervious surface, said process being substantially as hereinbefore described with reference to any one or more of the Examples. 28. A foamed rubber product or foamed plastic product sealed according to the process defined in any one of claims 1 to 19 or 27. 29. A formulation when used in the process defined in any one of claims 1 to 19 or 27, as substantially hereinbefore described with reference to any one of the Examples.

Inventors: SUTHERLAND EUAN, SUTHERLAND, EUAN
Applicants: COMMERCIAL BUREAU PTY LTD, DAR VINCI PTY LTD, SUTHERLAND EUAN, COMMERCIAL BUREAU PTY. LTD., DAR VINCI PTY. LTD., SUTHERLAND, EUAN
Application year: 1997
Main classification: C08J9
IPC codes: B29C44, C08J9