A METHOD OF PRODUCING AN EXPANDED FOAMED MATERIAL AND COMPONENTS AND APPARATUS FOR USE IN SUCH A METHOD

Abstract: A process for forming synthetic expanded or foamed materials, such as acid-cured foams, condensation polymers such as phenolic resins. Catalysts, blowing agents and combinations of the two are described along with apparatus for use in the process. The invention includes a process for the preparation of an expanded or foamed material, which comprises the expansion or foaming and subsequent hardening of a polymer or resin by the admixture of an expandable polymer or resin, a catalyst capable of causing hardening of the polymer or resin, a blowing agent capable of generating a gas within the polymer or resin so as to form cells therein and a surfactant capable of stabilising cells formed within the polymer or resin. The process is characterised in that the surfactant is substantially miscible with the blowing agent and the process involves the step of mixing the blowing agent with the surfactant prior to admixing those components with the resin and/or catalyst.

Description: A METHOD OF PRODUCING AN EXPANDED FOAMED MATERIAL AND COMPONENTS AND APPARATUS FOR USE IN SUCH A METHOD Field of the invention This invention relates to methods of forming foamed or expanded materials from synthetic polymers and resins and, more particularly, to methods of forming foamed or expanded materials from catalyst cured condensation polymers, particularly phenolic resins, such as phenol formaldehyde resins . Background The formation of expanded synthetic materials such as foams formed from acid-cured phenolic resins has been known for some considerable time but, despite historical developments, there still remain difficulties in producing material of consistently high quality, particularly by an injection process. As is well known, the formation of expanded materials such as rigid foams involves combining a suitable polymer or resin with a blowing agent, surfactant or cell stabiliser and catalyst. The blowing agent creates voids in the polymer or resin which are stabilised by the surfactant, while the polymer or resin cross-links and thus hardens under the influence of the catalyst . Producing phenolic resin foams poses particular problems. Firstly phenolic resins such as phenol formaldehyde resins and conventionally used acid curing catalysts contain water which is released from solution during the foam-forming process. In addition, the catalyst initiated cross-linking process releases further water. It has been found that the more water present or formed, the more that is potentially trapped in the foam and, thus, the more likely water-related defects are to arise in the foam. The likelihood of water- related defects has been found to be exacerbated by the small cell size of many phenolic resin foams with the result that consistently achieving foam with defect-free cells, in a typical environment, has been virtually impossible. Preferred applications for expanded materials such as phenolic resin foams are those which require, or at least seek, good thermal insulating properties, low flammability, and low smoke generation and low toxicity when combusted. High thermal insulation or low thermal conductivity of expanded materials is achieved from a combination of : 1) fine cell size; 2) defect-free, closed cells which limit the passage of gases through the material ; and 3) the thermal conductivity of the blowing gases (generally lower than air) trapped in the closed cells. Thermal conductivity will, however, generally increase with time as blowing gases, trapped within the closed cells during foam formation, diffuse through the cell walls. It has been observed that existing, commercially available, expanded materials such as phenolic resin foams all display significant degrees of defective cells and thus their ability to act as thermal insulators is potentially compromised. A further drawback of existing expanded foamed materials is that the processes for their formation do not provide adequate control over the structure of the finished material. It has been found that anisotropy arising from current processes typically leads to the formation of axes of minimum and maximum strength in cured phenolic resin foam. This must be borne in mind when specifying applications for such foam as, in many cases, because the axes of strength cannot be readily identified, application for the cured foam must be restricted to minimum observed strengths . Another significant characteristic of acid-cured resole phenolic resin foams is that they exhibit significant residual acidic activity. This acidity can limit their final application due to potential corrosive effects. Typical prior art methods in this field have been directed to the formation of expanded material such as rigid phenolic resin foam in the form of moulded blocks or continuous laminates which are subsequently cut or otherwise shaped for their intended application. Examples of both block and laminate formation are described in, for example, EP-A-0 170 357. The methods disclosed in EP-A-0 170 357 involve the use of strong mineral acids, such as sulphuric acid, as the catalyst and halogenated chlorofluorocarbons (CFCs) , in the form of freon, as the blowing agent. The use of sulphuric acid as the catalyst leads to the corrosive behaviour referred to above. Further, the use of CFCs in foam production is now considered unacceptable because, as is well documented , CFCs cause depletion of the Earth's ozone layer. A further example of phenolic resin foam production is disclosed in EP-A-0 439 283. The processes disclosed in this document replace CFCs as blowing agents with materials which are a mixture of perfluorohydrocarbons and hydrogenated chlorofluorocarbons . Otherwise the processes disclosed are largely conventional. The catalysts specified in this disclosure again comprise strong mineral acids such as sulphuric or hydrochloric acids although mention is also made of using aryl sulphonic acids such as p-toluene or xylene sulphonic acids in the role of catalyst . However these forms of sulphonic acid, as described, contain significant amounts of water. GB-A-2 232 673 discloses a further acid-cured phenolic resin foam process in which the blowing agent incorporates non-CFC components. Also included within the disclosure is considerable background information on the mechanisms involved in phenolic resin foam formation and on various factors which can influence the process outcome . With this in mind the contents of this disclosure are incorporated herein by reference. In all known prior art processes for the formation of expanded material, including those disclosed in EP-A-0 170 357, EP-A-0 439 283, and GB-A-2 232 673, the surfactant or cell stabiliser is premixed with the polymer or resin prior to the blowing agent and catalyst being added. This conventional premixing is considered by us to be responsible for certain types and degrees of cell defects typically found in expanded materials such as rigid phenolic resin foams . The surfactants used in expanded or foamed material are typically polar in nature and are often highly polar. More typically, one end of the surfactant molecule is hydrophilic while the other end is hydrophobic. We believe that the consequence of this is that, when premixed with a polymer resin to be expanded, the hydrophilic ends of many of the surfactant molecules are considered to attract water and retain that water in the system. Further, that the surfactant can stabilise air bubbles which form in the polymer or resin during the mixing process . The end result of both is that defects often arise in the cured foam. Further disadvantages have been found by us to arise from premixing a polymer or resin and surfactant prior to addition of blowing agent and catalyst. By way of example, as an acid catalyst is added to a resin/surfactant pre- mixture, the acidic nature of the catalyst breaks down or nullifies a proportion of surfactant and thus renders a significant amount of the surfactant incapable of performing its intended function. The consequence of this is that excess surfactant must be added to enable the foam formation process to proceed effectively. This, in turn, can have significant influence on process cost. Summary of invention It is a feature of this invention that embodiments thereof can provide a novel process, and materials and apparatus for use therein, for producing, on a reproducible basis and under factory conditions, expanded or foamed materials, such as an acid-cured rigid phenolic resin foam, having one or more of the following: a) substantially defect-free cells both in struts and windows, b) controlled cell structure (open, partially open or closed) c) reduced residual acidity to effectively eliminate or at least substantially reduce corrosive behaviour in many applications, d) reduced surfactant requirement, e) in block foam, reduced anisotropy and therefore density for a given strength, f) controlled anisotropy in injection moulded product, and g) good and preferably stable thermal conductivity characteristics . Embodiments of the invention may at least provide a novel process, materials and apparatus which will provide a useful choice or overcome or mitigate the problems associated with known expanded or foamed materials and processes for their formation. In particular there is provided a process which overcomes the problems involved in prior mixing the polymer or resin and surfactant. According to a first aspect of the present invention there is provided a process for the preparation of an expanded or foamed material, which process comprises the expansion or foaming and subsequent hardening of a polymer or resin by the admixture of an expandable polymer or resin, a catalyst capable of causing hardening of the polymer or resin, a blowing agent capable of generating a gas within the polymer or resin so as to form cells therein and a surfactant capable of stabilising cells formed within the polymer or resin, the process being characterised in that the surfactant is substantially miscible with the blowing agent and the process involves the step of mixing the blowing agent with the surfactant prior to admixing those components with the resin and/or catalyst. We have found that the premixture of the surfactant and blowing agent not only mitigates or avoids the disadvantages given above for the premixture of resin and surfactant, but also provides an advantageous protective effect on acid or otherwise sensitive surfactants and an advantageous lubricating effect making it easier to control processing. Preferably the process includes the further step of admixing the resin and the blowing agent/surfactant pre-mixture, at least in part, prior to introducing, i.e. admixture with, the catalyst . Suitable polymers or resins for use in the present invention will be well known to the skilled man and include synthetic polymers and resins formed from the condensation or polymerisation of suitable condensation or polymerisation reagents. Such condensation polymers and resins include polyurethane resins and polystyrene, polyether and polyisocyanate polymers. Particularly suitable are phenolic resins formed from the condensation of a phenol with an aldehyde. The phenol may be a substituted phenol such as resorcinol, xylenol or a cresol, or preferably is phenol itself. The aldehyde may be acetaldehyde (ethanal) , benzaldehyde, furfuraldehyde, paraformaldehyde or preferable formaldehyde (methanal) . Condensation of the phenol and aldehyde may take place under any suitable conditions. It may take place using either an acid or preferably a base condensation catalyst such as sodium hydroxide. It is particularly preferred that the resin be a resole phenol formaldehyde resin. Preferably the polymer or resin is a low free formaldehyde resin having a formaldehyde to phenol mole ratio within the range 1.3 to 2.0:1 and, more preferably, within the range 1.5 to 1.6:1. Suitable catalysts for use in the process will be well known to the skilled man and will depend on the nature of the polymer or resin or other ingredients to be used. They include organic or inorganic acids, including mineral acids such as sulphuric or hydrochloric acid and aryl (aromatic) sulphonic acids such as p-toluene, xylene or cumene sulphonic acids or combinations thereof. Preferably the catalyst is an aryl (aromatic) sulphonic acid or a combination of such acids. Such sulphonic acids are selected preferentially so as to be low in water content. Indeed, the water content of the catalyst is preferably close to or substantially zero. It is particularly preferred that the catalyst be a combination of benzene and xylene sulphonic acids. The combined acids are preferably mixed in ratios of benzene sulphonic acid to xylene sulphonic acid of 10 parts: 90 parts through to 90 parts: 10 parts. More preferred ranges are 30 parts: 70 parts through to 70 parts: 30 parts. For injection (fast reaction) processes, a greater proportion of benzene sulphonic acid is used whilst for block moulding applications (slow reaction) , a greater proportion of xylene sulphonic acid is used. Cumene, phenol and toluene sulphonic acids are possible substitutes and can assist with control of cell structure (open or closed) as well as influencing char characteristics under fire conditions. Preferably the catalyst further includes a proportion of orthophosphoric acid or other phosphorus containing compound. Suitable blowing agents for use in the present invention will be well known to the skilled man and will depend on the nature of the polymer or resin and the other ingredients being used. Suitable blowing agents include halogenated, particularly fluorinated, methane or ethane derivatives such as hydrofluorocarbons (HFCs) such as 134a, -245, -356, -365 and hydrogenated chlorofluorocarbons (HCFCs) for example HCFC 141b. Other options include dichloromethane, n-pentane and cyclopentane and may also include suitable hydrofluoroethers . Mixtures of blowing agents may also be used. A particularly preferred blowing agent comprises a blend of dichloromethane and one or more hydrofluoroethers . Suitable surfactants for use in the present invention will be well known to the skilled man and will depend on the nature of the polymer or resin and other ingredients being used. Suitable surfactants, or cell stabilisers, include silicones and alkoxylates or glycerides and mixtures thereof . Suitable silicones include polymeric or modified silicones such as polysiloxane or organomodified silicone fluid. Suitable alkoxylates include castor oil and ethoxylated castor oils and phenol ethoxylates such as nanyl phenol ethoxylate . Preferably the surfactant comprises a mixture of modified polysiloxanes (such as a polysiloxane and polyether copolymer) and alkoxlylates . Preferably the alkoxlylates comprise ethoxylated castor oils. Admixture of the ingredients and their subsequent foaming and curing (hardening) can be carried out by any suitable method such as those currently employed in the art and may involve a batch wise or continuous process. Preferably the process further comprises the step of cooling the mixture of blowing agent and surfactant to below the temperature of the polymer or resin and/or catalyst, before admixture of the blowing agent/surfactant pre-mixture with the polymer or resin and/or catalyst . A variety of adjuvants may be added to the ingredients at any stage during the process. Adjuvants, may be added for example to the individual ingredients prior to their admixture or to any combinations of the ingredients or to the combined admixture. Suitable adjuvants include solvents, viscosity modifiers, diluents, fillers, binders, reinforcing agents and reactivity control agents, e.g. for controlling the boiling point of the blowing agent. Alcohols and/or glycols may be added to the resin or polymer or to the catalyst so as to at least partially neutralise residual acidity of the foam mixture. The process preferably includes means for controlling the cell formation in the foam. Such means may include the step of reducing the vapour pressure of the blowing agent prior to combining the blowing agent/surfactant pre-mixture with the polymer or resin and/or the catalyst . For this purpose the process may include the step of cooling the blowing agent/surfactant pre-mixture to below the temperature of the polymer or resin and/or the catalyst, prior to mixing or alternatively or in addition pressurising the blowing agent/surfactant pre-mixture. It has been found that many of the defects of known expanded or foamed materials, in particular defects in cell structure, are due to the presence of excessive levels of water in the system to be used for the formation of the expanded or foamed material. It has been found particularly damaging if the polymer or resin and catalyst contains a large amount of water. As mentioned above this is a particular problem with phenolic resin systems where the condensation reaction for the formation of the phenolic resin inevitably leads to an inherent water content. There has now been found a means of avoiding defects, such as cell defects, in expanded or foamed material. According to a second aspect of the present invention there is provided a process for the preparation of an expanded or foamed material, which process comprises the expansion or foaming and subsequent hardening of a polymer or resin by the admixture of an expandable polymer or resin, a catalyst capable of causing hardening of the polymer or resin, a blowing agent capable of generating a gas within the polymer or resin so as to form cells therein and a surfactant capable of stabilising cells formed within the polymer or resin, the process being characterised in that the total water content of the polymer or resin and catalyst combined is no greater than 20% by total weight of those ingredients combined. By keeping the water content of the polymer or resin and catalyst below 20% it has been found that not only are the prior art problems of defective materials or cells mitigated or overcome, but in addition improved miscibility of the polymer or resin/catalyst system is unexpectedly achieved. The polymer or resin to be used should be chosen in a form having a minimum water content and aqueous ingredients, in particular solvents such as water, should be avoided so as to achieve the no greater than 20% water content. The polymer or resin, catalyst, blowing agent, surfactant and any adjuvants used and the process steps utilised may be substantially as described above for the first aspect of the invention. As the water content of the polymer or resin/catalyst combination should not be greater than 20%, it is preferred that the catalyst water content will generally be less than 5% by weight of the catalyst and more preferably, will be closer to or substantially at zero per cent. To keep the catalyst water content to a minimum it is preferred that an aromatic sulphonic acid or combinations of those acids be used as the catalyst. It is particularly preferred to use a combination of benzene and xylene sulphonic acids as mentioned above in relation to the first aspect of the invention. A process according to the second aspect of the present invention may be combined with a process according to the first aspect of the present invention as hereinbefore described. In prior art processes for the formation of expanded or foamed materials it has been known to add a solvent to the polymer or resin prior to its admixture with the surfactant and/or blowing agent. In the past, particularly in cases where the polymer or resin is a phenolic resin the solvent used has been water. We have found that the addition of such water leads to cell structure damage. A process has now been found which overcomes or mitigates the problems associated with the prior art addition of solvents. According to a third aspect of the present invention there is provided a process, for the preparation of an expanded or foamed material, which process comprises the expansion or foaming and subsequent hardening of a polymer or resin by the admixture of an expandable polymer or resin, a catalyst capable of causing hardening of the polymer or resin, a blowing agent capable of generating a gas within the polymer or resin so as to form cells therein and a surfactant capable of stabilising cells formed within the polymer or resin, the process being characterised in that it includes the further step of the addition of a solvent to the polymer or resin, the solvent being dichloromethane. It has been found that not only does the use of dichloromethane as a solvent for the polymer or resin avoid the prior art use of water and so lead to decreased cell defects but in addition has unexpected advantageous effects regarding viscosity of the system. The solvent may be added to the polymer or resin before or after the admixture with the catalyst and/or any other ingredients . The use of dichloromethane as a solvent is particularly advantageous where the polymer or resin is a phenolic resin such as a resole phenolic resin. The polymer or resin, catalyst, blowing agent, surfactant and any adjuvants used and the steps utilised may be substantially as described above for the first or second aspect of the invention. A process according to the third aspect of the invention may be combined with a process according to the first and/or second aspects hereinbefore described. In conventional processes for the production of expanded or foamed materials the catalyst of choice is a strong acid such as an aqueous mineral acid with aqueous sulphuric acid being the most common. The conventional use of this acid is disadvantageous in several respects and in particular because the resultant products have significant residual acidic activity leading to corrosive behaviour. A process has now been found which overcomes or mitigates the problems associates with the prior art use of catalysts. According to a fourth aspect of the present invention there is provided a process for the preparation of an expanded or foamed material, which process comprises the expansion or foaming and subsequent hardening of a polymer or resin by the admixture of an expandable polymer or resin, a catalyst capable of causing hardening of the polymer or resin, a blowing agent capable of generating a gas within the polymer or resin so as to form cells therein and a surfactant capable of stabilising cells formed within the polymer or resin, the process being characterised in that the catalyst used to harden the polymer or resin includes at least one aromatic sulphonic acid having substantially zero added mineral acid. The catalyst is an aromatic sulphonic acid such as p- toluene, xylene or cumene sulphonic acids or combinations thereof. Such sulphonic acids are selected preferentially so as to be low in water content. Indeed, the water content of the catalyst is preferably close to or substantially zero. It is particularly preferred that the catalyst be a combination of benzene and xylene sulphonic acids. The combined acids are preferably mixed in ratios of benzene sulphonic acid to xylene sulphonic acid of 10 parts: 90 parts through to 90 parts: 10 parts. More preferred ranges are 30 parts: 70 parts through to 70 parts: 30 parts. For injection (fast reaction) processes, a greater proportion of benzene sulphonic acid is used whilst for block moulding applications (slow reaction) , a greater proportion of xylene sulphonic acid is used. Cumene, phenol and toluene sulphonic acids are possible substitutes and can assist with control of cell structure (open or closed) as well as influencing char characteristics under fire conditions. Preferably the catalyst further includes a phosphorus containing compound, such as ortho-phosphoric acid. The ortho-phosphoric acid is preferably 85% food grade phosphoric acid and is mixed with the aromatic sulphonic acid(s) in the ratio of 20-50 parts ortho-phosphoric acid : 100 parts of sulphonic acid (e.g. benzene/xylene mix). It has been found that not only does a process according to the fourth aspect overcome or mitigate the problems associated with prior art catalysts such as residual acid activity but in addition leads to unexpected advantages such as improved miscibility of catalyst with the polymer or resin and/or other reagents, markedly decreased water levels and cell defects, and low corrosive characteristics. The use of at least one aromatic sulphonic acid, particularly when combined with a phosphorous containing compound such as food grade ortho-phosphate, allows leachable aggressive anions to be kept to a minimum resulting in excellent non- corrosive properties. Corrosion, particularly by pitting, of copper and iron is substantially eliminated. Further advantages include an improved effect on the exothermic nature of the foaming and hardening process and materials having improved reaction to fire including the reduction of punking . The polymer or resin, blowing agent, surfactant and any adjuvants used and the process steps utilised may be substantially as described above for the first, second and/or third aspects . A process according to the fourth aspect may be combined with a process according to one or more of the first, second and third aspects hereinbefore described. As mentioned above, existing, commercially available expanded materials display significant degrees of defective cells. It has been found that to avoid such defects careful choice has to be made of the blowing agent used. To avoid defects it has been found advantageous to use a blowing agent capable of forming closed cells in the polymer or resin. This is particularly difficult to do in the case of phenolic resins. There has now been found a process which overcomes these problems . According to a fifth aspect of the present invention there is provided a process for the preparation of an expanded or foamed material, which process comprises the expansion or foaming and subsequent hardening of a polymer or resin by the admixture of an expandable polymer or resin, a catalyst capable of causing hardening of the polymer or resin, a blowing agent capable of generating a gas within the polymer or resin so as to form cells therein and a surfactant capable of stabilising cells formed within the polymer or resin, the process being characterised in that the blowing agent includes or comprises dichloromethane and a hydrofluoroether miscible therein. Preferably the hydrofluoroether comprises HFE-7100 or HFE- 301 Speciality Fluid as sold by 3M. The polymer or resin, catalyst, surfactant and any adjuvants used and process steps utilised may be substantially as described above for the first to fourth aspects . The process of the fifth aspect may be used in combination with one or more of the first, second, third and fourth aspects of the present invention. According to a sixth aspect of the present invention there is provided a method of reducing the residual acidity of an acid cured phenolic resin foam, which method comprises the step of adding neutralising means to reduce residual acidity arising as a result of the resin-forming process or as a result of the foam-forming reaction. Preferably the method of the sixth aspect of the invention comprises the addition of one or more of : i) free phenol, ii) a low molecular weight condensation polymer, iii) an alcohol or glycol. The low molecular weight condensation polymer may comprise phenol formaldehyde, melamine formaldehyde or urea formaldehyde. The alcohol preferably comprises furfuryl alcohol. The method of the sixth aspect of the invention may be used in a process according to one or more of the first to fifth aspects of the invention when used to prepare a phenolic resin foam. According to a seventh aspect of the present invention there is provided a pre-mixture of blowing agent and surfactant for use in any of the processes or methods hereinbefore or hereinafter set forth. Preferably each of the said blowing agent and surfactant are as herein set forth. According to a eighth aspect of the present invention there is provided apparatus for producing an expanded or foamed material from the admixture of an expandable polymer or resin, a catalyst capable of causing hardening of the polymer or resin, a blowing agent capable of generating a gas within the polymer or resin so as to form cells therein and a surfactant capable of stabilising cells formed within the polymer or resin, which apparatus includes a mixing chamber; mixing means with the mixing chamber to effect intermixing of components supplied to the mixing chamber; first supply means constructed and arranged to supply polymer or resin into the mixing chamber; second supply means constructed and arranged to supply catalyst into the mixing chamber; and third supply means constructed and arranged to supply a mixture of blowing agent and surfactant to the mixing chamber. Preferably the first, second and third supply means include positive displacement pump means to enable metered quantities of each component to be supplied to the mixing chamber although, for foam applications in which the uncured foam mixture is dispensed in the absence of back-pressure, a variety of other pumps, such as gear/vane/lobe pumps, may be used. The preferred type of positive displacement pump is a piston pum . Preferably the third supply means further includes means to effect cooling of the blowing agent/surfactant mixture. Preferably the second supply means leads into the chamber at a position after there has been some mixing of the resin and the blowing agent/surfactant mixture. The processes, mixture and apparatus described herein can, with variations, be applied to: i) The manufacture of block foam for cut-to-size applications; ii) In-situ bonding of, for example, door and panel facings using an injection process; iii) The injection moulding of finished shapes, particularly with in-situ skins; iv) The continuous lamination of slab; and v) Hand or mechanical mixing before pouring into moulds . Description of the preferred embodiments Preferred processes, methods and apparatus according to the invention will now be described with reference to the accompanying drawing in which: Figure 1 : shows a process flow diagram for forming foam according to the invention: Figure 2: shows a schematic cross section of a typical mixing head useful in the performance of the invention: and Figure 3: shows a view along the line A-A in Figure 2. The invention relates to a process for producing foam from synthetic polymer or resin hereinafter simply "resin". As is well known to those skilled in the art, the formation of foam from synthetic resin involves combining the resin with a blowing agent to form cells, generally air-containing cells, within the resin whilst cross-linking the resin using a catalyst. A surfactant or cell stabiliser is also added to give stability to the cells during mixing formation and curing. Whilst the invention could have application to a number of resin/catalyst/blowing agent/surfactant systems, the invention has been developed particularly to allow the formation of stable, defect-free, rigid foam from acid-cured phenolic resins. Foam production from condensation polymers such as phenolic resins present particular problems, largely arising from the fact that the resins, and the catalysts typically used, contain significant amounts of water. Further water is produced as the cross-linking reaction proceeds. This water can become trapped during cell formation, often leading to defects in the windows and/or struts of the foam cells. The present invention, at least in the preferred embodiment described herein, combines careful selection of low water content components, a novel order of combination of components, temperature control and mixing control to ensure the production of stable, consistent, defect-free foams. Typical resins used in the process according to the invention are low free formaldehyde resoles with a solids content in excess of 70%. Suitable resoles typically have a formaldehyde to phenol mole ratio in the range 1.3 to 2.0 and more preferably in the range 1.5 to 1.6. Suitable resins are available on a commercial basis from manufacturers such as Hepworths Minerals & Chemicals Limited, Borden, BP Chemicals, Cray Valley, Schenectady and Bitrez . Depending on the intended application and/or process, viscosity and reaction controllers may be added to the resin. These are selected to balance with the chemistry of the intended catalyst . For moulding block foam one would select a heavily reacted (high viscosity) resin while for injection processes one would select a much less heavily reacted (lower viscosity) resin. As is implied, viscosity is a good measure of reactivity and may be adjusted using, for example, alcohols, particularly higher alcohols such as furfuryl alcohol; resorcinol and glycols. Furfuryl alcohol produces strong initial reactivity and is thus ideally suited to injection processes. Resorcinol is less reactive and has the added advantage that it provides a more controllable reactivity. Glycols are altogether less reactive and are thus ideally suited to block-forming processes. We have observed that the addition of additives such as alcohols and glycols, resorcinol and even free phenol, seems to reduce residual acidity and we believe this is because residual sulphuric acid, arising as a contaminant in the resin as part of the resin manufacturing process, is neutralized. The viscosity modifiers may also be used to assist control of the density of the foam. It will be appreciated that, if mechanical strength is important, then a denser foam is required. If thermal resistance is important then a lower density foam is required. Viscosity modifiers can be added to lower the processing temperature and thus enable higher density foams to be reproducibly achieved. Rather than the strong mineral acids typically used as catalysts heretofore, we have found that the objectives of the invention can more readily be achieved using aromatic sulphonic acids and, more particularly, low water content aromatic sulphonic acids. By "low water content", we mean a total system (resin + catalyst) water content of not greater than 20% and preferably less than 15%. In many cases this water will be present totally, or almost totally, in the resin leaving a need to select a basic catalyst having a water content as near as possible to zero. Useful catalysts according to this invention preferably comprise a mixture of sulphonic acids and, optionally, a proportion of ortho-phosphoric acid or similar. The ortho- phosphoric acid enhances the fire performance of the resulting foam, serves as a diluent to reduce the tendency of the low water content sulphonic acids to commence to crystallise and also influences reactivity. One feature of adding ortho-phosphoric acid is that a proportion of water is also added. Currently available ortho- phosphoric acids contain a minimum of 15% water and we select and use those which have the least water content . Suitable mixtures of sulphonic acids include benzene and xylene sulphonic acids in ratios falling in the range 10 parts : 90 parts though to 90 parts :10 parts. Preferred ranges are 90 15 parts :10 parts through to 70 parts : 30 parts and 30 parts : 70 parts through to 10 parts : 90 parts. For fast (injection) reactions a higher percentage of benzene is used whilst for slow (block) reactions, a higher percentage of xylene is used. Cumene, phenol and/or toluene sulphonic acids can be substituted for benzene and xylene. Partial substitution is most effective when the substitutes mentioned comprise 5 - 25% of the total sulphonic acid content. The above catalyst constituents can be combined as follows: Sulphonic acids: 100 parts Ortho-Phosphoric acid (optionally) : 20 - 50 parts When incorporating ortho-phosphoric acid, it should be borne in mind that some grades include impurities which we believe contribute to increase levels of certain leachants in the foam. For example, technical grades of phosphoric acid can contribute a few hundred ppm of sulphates and are not controlled with respect to chloride or nitrate content . However, we have found that food grade phosphoric acids make little contribution to leachant levels due to controlled anionic levels and species. The strongest food grade ortho-phosphoric acid (ie that having the lowest water content) which we have been able to source is 85%. The selection and combination of blowing agent and surfactant are extremely important. In accordance with one aspect of this invention, an essential feature is that the blowing agent and surfactant are pre-mixed prior to combination with the resin and catalyst. This is in contrast with prior art processes in which the surfactant is combined with the resin. Just as the resin with its viscosity/reaction modifiers is specified according to application and catalyst chemistry, so the specification of the blowing agent / surfactant mix is selected to balance with the resin and catalyst. Blowing agents used in performing the process according to the invention include hydro fluorocarbons, suitable examples of which are specified in the Montreal Protocol on Substances that Deplete the Ozone Layer. The Montreal Protocol specifically identifies HFCs -245, -356, -365. The processes described herein were initially devised based on the use of HCFC 141b as the blowing agent, but HCFC 141b can be replaced by dichloromethane, n-pentane or 25 cyclopentane . To these one can add perfluoro alkanes such as perfluoro pentane or perfluoro hexane . Other possible additives include hydrofluoroethers such as HFEs -7100 or -301 and HFE B manufactured by 3M, or hydrofluorocarbons such as 134a. The additives act as cell refiners in that they decrease surface tension to enhance cell stability. They also ensure minimal ozone depletion potential of blowing agent systems. We have found that particularly good results can be achieved using dichloromethane (DCM) as a blowing agent. DCM displays extremely useful processing characteristics, extremely good cell control characteristics when combined with certain hydrofluoroethers miscible therein, and has the advantage of having zero ozone depletion potential. Suitable hydrofluoroethers for cell control include HFE-7100 and HFE301 manufactured by the 3M Company. The processing advantages from using DCM are believed to arise because DCM is at least partially soluble in the resole phenolic resins of the types used for foam production, and can thus also serve, to some extent, as a viscosity adjuster. We have found that the use of DCM as a blowing agent generates less heat during mixing than other blowing agents and permits better control over the thermal balance of the system. There are two basic types of surfactant or cell stabiliser useful in the present invention, namely polysiloxanes and alkoxlylates. The polysiloxanes are more expensive but are able to react into the cured resin and reduce brittleness. Mixes of surfactants need to be provided so as to ensure stability of the blowing agent through a changing pH spectrum, changing phase, and changing temperature. The surfactant mixture must be able to: (i) Maintain stability of the blowing agent up to the maximum reaction temperature, (ii) Stabilise cell windows, and (iii) Contribute to the control mechanism which enables water to exit from the foam (thereby reducing cell defects) . Suitable polysiloxanes comprise those from the TEGOSTAB range of T H Goldschmidt whilst suitable alkoxlylates comprise ethoxylated castor oils from the ETHYLAN range of Akros. These are selected as they are substantially soluble in the blowing agent and effect the required control over cell formation under the full range of described conditions. The resin, catalyst, blowing agent and surfactant are combined as follows: Unlike prior art foam forming processes, the surfactant is not pre-mixed with the resin. It is our current belief that premixing a polar (often highly polar) surfactant with the resin is responsible for many of the defects which we have observed in foams formed using prior art processes. As a consequence, according to a first aspect of the invention we pre-mix the surfactant with the blowing agent and have observed a number of advantages in so doing. First, we believe that surfactant pre-mixed into resin tends to stabilise air bubbles formed in the resin during the mixing process, which air bubbles can lead to defects in the cured foam. Also, we suspect that pre-mixing surfactant in the resin tends to hold water in the system leading to further defects in the cured foam. Since pre-mixing the surfactant with the blowing agent, we have observed that mixing proceeds without the same retention of air bubbles and that the cell windows and struts in the cured foam display far less defects and incipient defects due to water retention. We believe that pre-mixing the surfactant with the blowing agent internally stabilises the cells as they form and thus significant contact with the resin is avoided. Hence micelle formations giving stabilised water droplets are less likely. As a consequence, the resin gives up a greater percentage of the molecular water contained therein and cell defects due to water retention are minimised if not avoided. Pre-mixing surfactant with the resin also leads to wastage of the surfactant because, under the influence of the acidic catalyst, the surfactant reacts and becomes inactive. Obviously it is necessary to exceed a minimal concentration of surfactant throughout the resin, before the surfactant can perform its intended function. By pre-mixing with the blowing agent, the surfactant is not only kept out of contact with the acid but also placed directly where it is needed. Thus, substantially more of the surfactant performs its intended function. In confirmation of this, we have found that defect free foams can be formed according to the invention using approximately half, or even less, of the quantity of surfactant used in prior art processes. For example, we have found that defect free foams can be produced with a surfactant level of from less than 1 to about 1.5 parts per 100 parts of resin for low reactivity (block) systems and about 1.0 to 3 parts per 100 parts of resin for high reactivity (injection) systems. In contrast, prior art methods in which the surfactant is pre-mixed with the resin typically require a surfactant content of 3 to 6% depending on the degree of reactivity required. Finally, we have observed that mixing the surfactant with the blowing agent improves the flowability of the total system. Blowing agents have a high vapour pressure, low viscosity and poor lubricating properties, the combination of which makes them difficult to handle, particularly to pump. By mixing the blowing agent with the surfactant, handling becomes much easier. Thus, in another aspect, the invention envisages reducing the vapour pressure of the blowing agent, by mixing the blowing agent with the surfactant. This objective may be further enhanced by increasing the external pressure i.e. by feeding the blowing agent/surfactant mixture from a pressurised source. Turning now to Figure 1, the invention further provides apparatus for performing the process hereinbefore described. As can be seen, the apparatus comprises a mixing chamber 10; mixing means 11 (fig 2) within said chamber 10 to effect mixing of materials placed within the chamber: first supply means, generally designated 12, to supply resin (hereinafter called Part A) into the chamber 10; second supply means, generally designated 14, to supply catalyst (hereinafter called Part B) into the chamber 10; and third supply means, generally designated 14, to supply a mixture of blowing agent and surfactant (hereinafter called Part C) into the chamber 10. In the form shown each of the supply means 12, 13 and 14 include feed tanks 12a, 13a and 14a which are charged with Parts A, B and C respectively from suitable storage facilities (not shown) . Feed pumps 12b, 13b and 14b then convey their respective materials to metering pumps 12c, 13c and 14c. Pumps 12c, 13c and 14c are preferably of the positive displacement type so as to ensure metered amounts of Parts A, B and C are fed into the mixing chamber 10. However, if the foam mixture is dispensed at ambient pressure (there is no back pressure on the system) other pump types such as vane, lobe or gear pumps, may be used. As an alternative, the apparatus might include some other form of flow control system operating on the feed pumps to ensure precise amounts of each component are delivered into the mixing chamber 10. The metering pumps may, for example, comprise piston pumps operated by a common linkage to ensure simultaneous delivery of Parts A, B and C to the chamber 10. The benefit of using piston pumps, or other forms of positive displacement pump, is that strict control can be maintained over component ratios and each component can be dispensed in accurately metered quantities even in the presence of back pressure. Interposed between each metering pump and the mixing head is a recirculation valve 12d, 13d and 14d to allow the components to be circulated through the system between mixing and injection steps and thus ensure consistent conditions are maintained at all times. Careful control of the components throughout the process is considered important and to this end temperatures and pressures are monitored and controlled. Feed tanks may be provided with suitable heating/ cooling apparatus (not shown) to enable temperatures to be established and controlled. Suitable feed temperatures and pressures are as follows : Part A Part B Part C Temp 17 ± 1 °C 12 ± 1 °C -10 to + 10 ± 2°C Pressure 0 - 2 bar 0 - 2 bar 2 - 5 bar In all cases control of the material parameters is readily effected by viscosity control (in turn related to process temperature and the reactivity of the resin) and all components are constantly stirred. Minimum feed pressure is 1 to 3 bar. The metering pumps 12c, 13c and 14c are set to deliver their respective materials to the mixing chamber in the following proportions although these ratios may vary according to the type of foam required: Part A 100 parts Part B 3 to 15 parts Part C 5 to 25 parts. The precise amount of Part C will depend on the total resin content because, as stated above, we want the amount of surfactant to comprise about 2% or less by weight of the total weight of resin. Further, the amount of blowing agent controls the foam density. Referring to Figures 2 and 3, the mixing means 11 preferably comprise a combination of rotating and static tines. These tines mix Parts A, B and C as they enter, and pass down, the chamber 10 thereby forming a uniform flowable cream. The rotating tines are mounted on a central rotating shaft 15 whilst the static tines project radially inwardly from the wall defining the chamber 10. The static and rotating tines are arranged so as to impart a shearing action to the cream passing through the chamber 10. The parts A, B, and C are fed into a cavity 16 at the upper end of the chamber 10 through ports formed in the wall defining the cavity 16. Referring to Figure 3 , the Part A component is fed through port 17, Part C is fed through port 18 and Part B through port 19. It will be appreciated that, with the arrangement shown in Figures 2 and 3 , there will be some mixing of Parts A and C before contact is made with Part B. This reduces the exposure of the surfactant to the acid catalyst and encourages the formation of stable blowing agent droplets. Depending on the nature of the cells required in the cured foam, the mixing chamber can be internally pressurised by providing a restricting nozzle 20 at the outlet thereof. The application of pressure prevents the formation of a vapour phase in the cream and therefore results in the formation of finer cells in the foam. After thorough mixing within the chamber 10 to commence the foaming reaction, yet preventing excessive heat build up, the resulting cream is released through restricting nozzle 20 and thereafter flows into the mould cavity 21 which is at atmospheric pressure or slightly higher due to injection displacement effects. For block formation, the cream is pumped into an insulated mould at ambient temperature. Before the mould is filled it is lined with polyethylene film and, after filling, the top of the foam is also covered with polyethylene film. This ensures water retention during initial curing. The foam is held in the mould for up to 24 hours or even longer, depending on the other curing parameters. This reduces anisotropy in the foam as can be shown by visual inspection of the cells and by mechanical testing. After release from the mould, the foam is subjected to further stabilisation for 7 days, held at ambient temperature or in an oven at about 40°C. For typical injected panels, the cream is injected into the panel cavity, the skins which define the cavity being in contact with platens held at a suitable temperature, typically in the range 30 to 50°C and more typically about 40°C. Under such conditions, the foam cures in less than 15 minutes, the differences from block arising because of the different foam component specifications and the typical differences in volume : surface area ratios of the end products. Example 1 The process according to the invention was used to fill, by foam injection, the cavity of a building panel. A cassette system using aluminium box section, faced with a suitable release system, to separate facing sheets of 8mm thick cement bonded particle board and fixed to a base of high performance birch ply (also coated with a release system), is placed between the heated platens of a press. The platens ensure that the facing sheets are maintained parallel to one another during injection, expansion and curing of the foam and are also used to control the temperature of the system, particularly at the interface thus controlling bond efficiency. Materials are prepared as follows: Part A: PA147 Resin (Borden) 100 parts ) Furfuryl alcohol 1 part ) Temp 16°C Resorcinol 1 part ) Part B: Equal parts of low water content benzene & xylene sulphonic acids 100 parts ) 1.75sg ortho- ) Temp 15°C phosphoric acid 30 parts ) Part C TEGOSTAB B8472 8.6 parts ) ETHYLAN C40AH 8.6 parts ) TEGOSTAB B8473 1.6 parts ) Carbon black dispersed )Temp-8°C in C40AH 2.6 parts ) HCFC 141b 100 parts ) 3M brand HFE 301 7.5 parts ) Calibration ratios: Part A : Part B : Part C =100 : 9.4 : 16.5 giving: Resin : Surfactant ratio of 100 : 2.7 or Part A : surfactant ratio of 100 : 2.65 Injection procedure: The loaded cassette is pre-heated to 40°C and held in the press at a pressure in the range 0.5 to 5 bar, preferably about 1 bar. Parts A, B and C are combined in a mixing chamber as above described to achieve a cream of uniform consistency. For every cubic metre of void space to be filled, a cream volume equivalent to 55kg of Part A is injected. For filling rectangular panels or doors, injection can be made through a hole provided in any edge, fine air bleed holes being positioned at the corners of the cassette. For a typical panel comprising facing sheets of 8mm cement bonded particle board, being 2.4m by 1.2 m in plan and having an overall thickness of 75mm, the cavity volume is 0.17 m 3 and thus requires 8.5kg of Part A and corresponding amounts of 20 Parts B and C. After filling, the cassette is held in the press for 10 to 15 minutes to allow the foam fully to cure. Example 2 Using commercial block resin PIF 301 (ex Borden) samples were produced with a fixed level of dipropylene glycol (DPG) added to reduce viscosity. The specifications of the three base components were: Part A PIF 301 Resin + 8% DPG + 1% Resorcinol. Part B Mixed xylene and benzene sulphonic acids (50/50) + 20% w/w 1.75 sg phosphoric acid. Part C Blowing agent (BA) : 100 parts 141b and 5 parts PP1S (ex British Nuclear Fuels Limited) Surfactant: TEGOSTAB B8473 ) Surfactant ETHYLAN C40AH ) concentrate TEGOSTAB B8472 ) mixture (SCM) Ratio of BA : SCM =14:2 Ratios: Part A : Part B : Part C =100 : 4.8 : 14.1 Giving: Part A : BA : SCM =100 : 12.3 : 1.8 As can be seen, the end surfactant level is very low when compared with prior art foams. Foams produced according to the invention display increased pH and dramatically reduced leachable ionic species when compared with prior art foams . Samples yielding S04 ions at levels below lOppm were achieved by combining linear alcohol into a mixture of xylene sulphonic acid and food grade phosphoric acid together with DPG and Resorcinol in the resin. In the samples itemised in Table 1, Part C consisted of various ratios of HCFC : HFA blowing agents (not critical) and combinations of silicone surfactants B8473 and B8472 with C40AH Example 3 Samples of commercially available phenolic foams, designated PA 1, PA 2 and PA 3 were taken and subjected to leaching extraction testing as hereinafter described. 5g of dry foam was ground and dissolved in 100ml of de- ionised water at room temperature for 6 hours. Samples were taken avoiding surface effects and contaminants . pH was monitored over the 6 hours. The effects of cell structure were eliminated by the use of ground, weighed samples. Further, samples of leachant were decanted and diluted to analyse for anion levels using DYNEX ion chromatography. The results are given in Table 1. The same procedures were applied to 14 samples of foams produced according to the invention, the results of which are shown as Inv 1 to Inv 14 in Table 1. Foams PA 1, PA 2 and PA 3 produced initial leachant values in the range 1.95 to 2.5 while those produced according to the invention yielded initial pH values in the less acidic range 2.5 to 3.4. After 6 hours these ranges had adjusted to 1.55 to 1.85 and 2.2 to 3.05 respectively, as can be seen from Table 1 . Anion analysis indicates the considerable difference between prior art commercial samples and those produced according to the invention. Variations in the latter are largely due to a combination of sulphonic acid types, and alcohols, used. Samples Inv 2 and Inv 4 demonstrate the effect of sulphonic acid type. Although pH values are similar, Inv 4 (embodying phenol sulphonic acid) exhibits particularly high sulphate levels compared to the others . Inv 2 included the addition of an alcohol and gave a lower value than Inv 3 using similar sulphonic acids (predominantly xylene sulphonic acid) but Inv 3 having no alcohol addition. All of samples Inv 8 to Inv 13 included, in addition, a combination of glycol and alcohol at 8.5% and 3% respectively, in the resin. The effect on corrosion of a piece of copper pipe was demonstrated using low level (circa 0.001 amp) galvanostatic conditions . Samples of foam (each of 3.3g), cut to closely fit identical lengths of 15mm diameter copper pipe, were placed in contact with a carefully cleaned sample of such pipe and immersed in 570g of de-mineralised water, the copper pipe being made the anode of a cell. The other electrode was similar, carefully cleaned, piece of copper pipe. Foam samples selected were PA 2 and PA 3 of the prior art samples and Inv 3 of the foams produced according to the invention. Each sample was tested for 24 hours, carefully washed with demineralised water, and examined. The electrolytes were also examined. It was apparent that the electrolyte of PA 3 had turned a strong blue, that of PA 2 a moderate blue and that of Inv 3 was little changed. Similarly the copper pipe in contact with PA3 displayed severe pitting, that in contact with PA2 moderately severe pitting and that in contact with Inv 3, no apparent pitting. Example 4 A block foam sample was prepared in accordance with the invention to test for particular leachant extractables. The results were compared with those derived from a commercially available (prior art) foam. The invention sample was prepared as follows Part A: IR5306 [Hepworths) Resin + 5% dipropylene glycol +0.75% carbon black. Part B : Benzene sulphonic acid 1 part Xylene sulphonic acid 7 parts 1.7sg ortho-phosphoric acid 4 parts Part C: Dichloromethane 16.1 parts HFE 7100 (ex 3M) 0.5 parts AKROS C40AH 2.7 parts AKROS C70AH 2.7 parts TEGOSTAB B8473 5.4 parts TEGOSTAB B8472 1.0 parts Mixer Speed Setting: 7 ( lOOOrpm) Part A output : 7.9 Kg/min Part B output: 395g/min Part C output: 948g/min Foam density was determined to be 37Kg/cubic metre A sample was taken from the above block foam and nitrate and sulphate leachables measured. These were compared with leachables measured from a sample taken from a commercially available foam slab having a density of 39Kg/cubic metre. The results were: Invention Prior Art Nitrates 0.22 ppm 0.31 ppm Sulphate 1070 ppm 6060 ppm It will thus be appreciated that the invention, at least as exemplified in the preferred embodiments described herein, and as confirmed by the examples and extract data, provides one or more of the following advantages : i) The process is applicable both to block moulding (slow) , continuous lamination (medium) and injection (fast) systems. ii) Whether a slow or a fast system is selected, cured foams display defect-free cells. As a consequence, if process parameters have been selected to produce a closed cell foam, foams of low thermal conductivity can be achieved on a reliable and reproducible basis. iii) The process uses significantly lower levels of surfactant resulting in real cost savings at current material prices. (iv) foams formed using the process described herein show markedly reduced levels of acidity and leachant activity and thus can be used in a wider variety of applications where corrosion is a consideration. (v) In fire tests, samples of foam produced as described herein show superior char stability and comply with a wide range of fire-related safe use requirements. TABLE 1 LEACHANT ANALYSIS Ionic Species ppm Sample Cl Br NO H PO SO pH PA 1 64.87 0.67 3.617 11.78 1671.6 1.85 PA 2 47.67 1.65 3.53 37.15 1351.7 1.85 PA 3 131.72 0.40 7.455 281.90 2696.9 1.55 Inv 1 10.52 0.00 0.174 153.60 162.10 2.40 Inv 2 11.04 0.068 0.690 161.80 23.88 2.00 Inv 3 10.02 0.023 0.353 149.9 173.39 2.30 Inv 4 11.59 0.019 0.157 164.3 288.30 2.20 Inv 5 100.50 0.50 0.846 95.97 66.77 2.40 Inv 6 9.603 0.132 0.135 106.70 127.7 2.30 Inv 7 16.135 0.644 0.688 137.50 73.22 2.50 Inv 8 0.921 0.027 0.088 7.172 2.327 2.85 Inv 9 25.34 0.03 0.067 5.188 1.649 3.05 Inv 10 0.865 <0.01 0.088 4.441 1.861 2.95 Inv 11 3.179 0.04 0.065 9.27 3.063 2.85 Inv 12 1.066 0.00 0.067 9.865 2.5621 2.55 Inv 13 1.038 0.00 0.15 9.946 2.644 2.65 Inv 14 0.751 0.00 0.05 0.253 73.38 2.50

Claims: CLAIMS 1. A process for the preparation of an expanded or foamed material, which process comprises the expansion or foaming and subsequent hardening of a polymer or resin by the admixture of an expandable polymer or resin, a catalyst capable of causing hardening of the polymer or resin, a blowing agent capable of generating a gas within the polymer or resin so as to form cells therein and a surfactant capable of stabilising cells formed within the polymer or resin, the process being characterised in that the surfactant is substantially miscible with the blowing agent and the process involves the step of mixing the blowing agent with the surfactant prior to admixing those components with the polymer or resin and/or catalyst . 2. A process according to Claim 1, which includes the further step of admixing the polymer or resin with the blowing agent/surfactant pre-mixture, at least in part, prior to admixture with the catalyst . 3. A process for the preparation of an expanded or foamed material, which process comprises the expansion or foaming and subsequent hardening of a polymer or resin by the admixture of an expandable polymer or resin, a catalyst capable of causing hardening of the polymer or resin, a blowing agent capable of generating a gas within the polymer or resin so as to form cells therein and a surfactant capable of stabilising cells formed within the polymer or resin, the process being characterised in that the total water content of the polymer or resin and catalyst combined is no greater than 20% by total weight of those ingredients combined. 4. A process according to Claim 1, 2 or 3 in which the catalyst is an acidic catalyst having a water content of less than 5%. 5. A process according to any preceding claim, wherein the polymer or resin is a phenolic resin. 6. A process according to Claim 5, wherein the resin is a low free formaldehyde phenolic resin having a formaldehyde to phenol mole ratio within the range 1.3 to 2.0. 7. A process according to Claim 6, wherein the formaldehyde to phenol mole ratio lies within the range 1.5 to 1.6. 8. A process according to any preceding claim, which further includes adding viscosity and reactivity control additives to the polymer or resin. 9. A process according to any preceding claim, wherein the catalyst is one or more aromatic sulphonic acids the catalyst having a water content of substantially zero. 10. A process according to Claim 9, wherein the aromatic sulphonic acids comprise benzene and xylene sulphonic acids respectively mixed in ratios 10 parts : 90 parts through to 90 parts : 10 parts. 11. A process according to Claim 10, wherein the respective ratios are 30 parts : 70 parts through to 70 parts : 30 parts. 12. A process according to any of claims 9, 10 or 11, wherein the catalyst further includes a proportion of ortho-phosphoric acid or other phosphorous containing compound . 13. A process according to any preceding claim, wherein the blowing agent is selected from a group which includes HFCs -134a, -245, -356, -365 and HCFC 141b. 14. A process according to any one of claims 1 to 12, wherein the blowing agent includes dichloromethane . 15. A process according to Claim 14, wherein the blowing agent comprises a blend of dichloromethane and one or more hydrofluoroethers. 16. A process according to any preceding claim, wherein the surfactant comprises a mixture of modified polysiloxanes and alkoxlylates. 17. A process according to Claim 16, wherein the alkoxlylates comprise ethoxylated castor oils. 18. A process according to any preceding claim, which further includes adding alcohols and/or glycols to the polymer or resin or to the catalyst so as to at least partially neutralise any residual acidity of the foam mixture . 19. A process according to any preceding claim, which further includes the step of cooling the pre-mixture of blowing agent and surfactant to below the temperature of the polymer or resin and/or of the catalyst, before combining the pre-mixture with the polymer or resin and/or the catalyst . 20. A method of controlling cell formation in a foam produced according to any of Claims 1 to 19, which method includes reducing the vapour pressure of the blowing agent prior to combining the blowing agent/surfactant pre-mixture with the polymer or resin and/or the catalyst . 21. A method according to Claim 20, which includes cooling the blowing agent/surfactant mixture to below the temperature of the polymer or resin and/or of the catalyst, prior to admixing it with the polymer or resin and/or the catalyst . 22. A method according to Claim 20 or Claim 21, which includes pressurising the blowing agent/surfactant mixture . 23. A method of reducing the residual acidity of an acid cured phenolic resin foam, which method comprises the step of adding neutralising means to reduce residual acidity arising as a result of the resin-forming process or as a result of the foam-forming reaction. 24. A method according to Claim 23, wherein the neutralising means comprise one or more of: i) free phenol, ii) a low molecular weight condensation polymer, iii) an alcohol or glycol. 25. A method according to Claim 24, wherein the low molecular weight condensation polymer comprises phenol formaldehyde, melamine formaldehyde or urea formaldehyde. 26. A method according to Claim 24 or Claim 25, wherein the alcohol comprises furfuryl alcohol. 27. A process for the preparation of an expanded or foamed material, which process comprises the expansion or foaming and subsequent hardening of a polymer or resin by the admixture of an expandable polymer or resin, a catalyst capable of causing hardening of the polymer or resin, a blowing agent capable of generating a gas within the polymer or resin so as to form cells therein and a surfactant capable of stabilising cells formed within the polymer or resin, which process is characterised in that the catalyst used to harden the polymer or resin includes one or more aromatic sulphonic acids having substantially zero added mineral acid. 28. A process according to Claim 27, wherein the process constituents are selected to provide a total water content of less than 20%. 29. A process according to Claim 27 or Claim 28, wherein the catalyst includes a mixture of benzene and xylene sulphonic acids. 30. A process according to Claim 29, wherein the ratio of benzene :xylene sulphonic acids falls in the range 90 parts: 10 parts through to 10 parts: 90 parts respectively. 31. A process according to Claim 30, wherein the ratio falls in the range 70 parts: 30 parts through to 30 parts: 70 parts. 32. A process according to any one of Claims 27 to 31, wherein the catalyst further includes ortho-phosphoric acid. 33. A process according to Claim 32, wherein the phosphoric acid comprises 85% food grade phosphoric acid and is mixed with the sulphonic acids in the ratio 20 - 50 parts ortho-phosphoric acid: 100 parts of sulphonic acid. 34. A process for the preparation of an expanded or foamed material, which process comprises the expansion or foaming and subsequent hardening of a polymer or resin by the admixture of an expandable polymer or resin, a catalyst capable of causing hardening of the polymer or resin, a blowing agent capable of generating a gas within the polymer or resin so as to form cells therein and a surfactant capable of stabilising cells formed within the polymer or resin, characterised in that the blowing agent includes dichloromethane and one or more hydrofluoroethers miscible therein. 35. A process according to Claim 34, wherein the hydrofluoroether comprises HFE-7100 or HFE-301 Specialty Fluid as sold by 3M™. 36. A process for the preparation of an expanded or foamed material, which process comprises the expansion or foaming and subsequent hardening of a polymer or resin by the admixture of an expandable polymer or resin, a catalyst capable of causing hardening of the polymer or resin, a blowing agent capable of generating a gas within the polymer or resin so as to form cells therein and a surfactant capable of stabilising cells formed within the polymer or resin, , characterised in that the process includes the further step of the addition of a solvent to the polymer or resin, the solvent being dichloromethane. 37. A pre-mixture of blowing agent and surfactant for use in a process according to any one of Claims 1 to 36. 38. Apparatus for producing expanded foamed material from the admixture and subsequent foaming and hardening of an expandable polymer or resin or a catalyst capable of causing hardening of the polymer or resin, a blowing agent capable of generating gas within the polymer or resin so as to produce cells therein, and a surfactant capable of stabilising cells formed within the polymer or resin, the apparatus including a mixing chamber; mixing means within the mixing chamber to effect intermixing of components supplied to the mixing chamber; first supply means constructed and arranged to supply resin into the mixing chamber; second supply means constructed and arranged to supply catalyst into the mixing chamber; and third supply means constructed and arranged to supply a mixture of blowing agent and surfactant to the mixing chamber . 39. Apparatus according to Claim 38, wherein the first, second and third supply means include positive displacement pump means to enable metered quantities of each component to be supplied to the mixing chamber. 40. Apparatus according to Claim 39, wherein the positive displacement pump means comprise a piston pump 41. Apparatus according to any one of Claims 38 to 40, wherein the third supply means further includes means to effect cooling of the blowing agent/surfactant mixture. 42. Apparatus according to any one of Claims 38 to 41, wherein the second supply means leads into the chamber at a position after there has been some mixing of the resin and the blowing agent/surfactant mixture.

Inventors: EVANS ALBERT EDWARD JOHN, HARRIS ANDREW JOHN, EVANS, ALBERT, EDWARD, JOHN, HARRIS, ANDREW, JOHN
Applicants: EVANS ALBERT E J, HARRIS ANDREW J, EVANS, ALBERT, EDWARD, JOHN, HARRIS, ANDREW, JOHN
Application year: 1998
Main classification: C08J9
IPC codes: B29C44, C08J9