Semiflexible or flexible resin compositions

Abstract: A phenolic resin (novalak or resol) is prepared, preferably from formaldehyde; 100 parts by wt. are mixed with 0.5 to 20 parts of a surfactant (e.g. a polyoxyethy­ lene compound), 1 to 20 parts of a blowing agent (a vola­ tile liquid) and optionally 0.5 to 10 parts of a wetting agent which acts to open the cells (e.g. sodium or ammonium lauryl ether sulphate), the mixing is at high speed and high shear. Separately an acid catalyst is prepared, e.g. of sulphonic acids and phosphoric acid, and the mixtures admixed so as to cure the resin, e.g. for 1/2-24 hours at room temperature to 65°C. The cured cellular product is cut into a sheet and compressed, e. g. between two plates, to e.g. 5 to 60%, preferably 50-60% of its original thickness, for from 2 to 60 seconds, and the pressure released. The sheet regains 50-95% of its original thickness and remains flexible or semi-flexible. The product has properties suitable for its use in insulation, absorption of fluids or sound, or cushioning. A substance which improves resistance to fire and smoke can optionally be incorporated.

Description: The present invention relates to semi-flexible or flexible phenolic foams having a substantially open cellular structure and to a process for preparing them. The foam material of the present invention can be used for insulation, fluid absorption, sound absorption, cushioning and other applications. Phenolic resinous compositions were produced for the first time at the beginning of the 20th century after A. von Baeyer had discovered the reaction between phenols and aldehydes in 1872. In recent years, there has been an increased interest in phenolic polymers which can be formed into cellular materials; these are commonly referred to as phenolic foams. Since phenolic foams were mainly considered as good insulating products possessing excellent flame-resistant properties, most of the research conducted on them over the past decades has been directed to improving these properties. Prior to 1968, it was generally taught to use thermosetting phenolic resin foam structures that could be prepared by reacting an acid catalyst with a heat hardenable phenol-aldehyde one-step resin, commonly called "resol". Resols and novolaks are products of the reaction of phenols with formaldehyde and these resins have been used for a variety of purposes. Although resols are normally made with formaldehyde, other aldehydes are often used if certain desired characteristics are required for the resulting phenolic resin product. A resol can be defined as a synthetic resin produced from a phenol and an aldehyde; its molecule contains reactive methylol or substituted methylol groups. Heating causes the reactive resol molecules to condense together to form larger molecules. This result is achieved without the addition of any substances containing reactive methylene or substituted methylene groups. As for a novolak, it is a soluble fusible synthetic resin also produced from a phenol and an aldehyde. However, the novolak molecule does not contain any reactive methylol or substituted methylol groups and is therefore incapable of condensing with other novolak molecules on heating without the addition of hardening agents. The reaction of an acidic catalyst with a resol resin being exothermic, this creates sufficient heat to convert the water of condensation and any water initially present in the mixture to steam. This steam, which is usually uniformly distributed throughout the resin, foams the reacting resin into a frothy mass and because of the rapid exotherm, the resin converts quickly into an infusible condition before the froth can collapse to any significant extent because of the condensation of the steam. The foam resulting from this type of process was referred to as an "open cell" foam. This type of foam was believed to be undesirable since it did not possess uniform insulating properties. In an attempt to develop a phenolic foam having improved insulation and flame-retarding properties, D'Alessandro produced an improved phenolic resin foam using polyhalogenated saturated fluorocarbons to produce a fine uniform closed cell structure in the phenolic foam. The retention of fluorocarbons in the closed cell structure led to a higher insulation value. Since the D'Alessandro patent, it has been established that fluorocarbon blowing agents contribute to damaging the ozone layer of the earth's atmosphere. Therefore, other suitable commercial alternatives need to be sought. Also, the brittleness of the rigid phenolic foams closed or open cell was a major inconvenience. In 1975, Ernest K. Moss in U.S. Patent 3,876,620 attempted to solve this problem by introducing a phenolic polymer exhibiting a friability of less than 15% when formed into a cellular product. This was achieved by using o-cresol in the phenolic composition. In 1979, Ernest K. Moss and John Beale in U.S. Patent 4,133,931 further improved on the 1975 Moss invention by providing an improved closed cell phenolic-resin foam material which exhibited low thermal conductivity without adversely affecting friability, compressive strength and the usual low flammability characteristics of this type of material. In this case, good results were achieved by using a branched non-ionic surfactant, but now undesirable fluorocarbons were used as blowing agents. In 1981 , Gusmer, in U.S. Patent 4,303,758, disclosed a novel technique through which a closed cell phenol-aldehyde foam product could be obtained. This method involved a frothing and curing technique that was designed by the inventor. Although phenolic foams have been known and available for many years, they were not much used for thermal insulation until only recently. Two major drawbacks made the commercialization of closed cell phenolic foams for thermal insulation difficult. First, closed cell cellular foams tend to loose their insulating properties over time because the brittleness of their structure inevitably leads to the partial breakdown of the closed cell network, thereby releasing from these cells the entrapped fluorocarbons which contribute to enhance the thermal insulation properties of the foam. Also, since all phenolic foams hitherto described are rigid, their compressive strength is usually quite limited and most often unsuitable for normal handling unless extreme care is taken in manipulating the product. As mentioned earlier, the general composition and method for preparing phenolic foams are well known. Generally speaking, a foamable phenolic resole composition is prepared by admixing a liquid phenolic resole, a blowing agent, a surfactant, and optional additives as well as an acid curing agent into a substantially uniform composition. The curing catalyst is usually added in amounts sufficient to initiate the highly exothermic curing reaction. This step, usually referred to as the foaming step, is most often conducted or performed in a cavity mold or a continuous laminating machine. When it is desired to manufacture phenolic foam insulation boards, the various ingredients are mixed until a substantially uniform composition is obtained. This composition is then applied onto a protective covering such as cardboard to which it will initially adhere. The foam is then covered with an other protective covering such as cardboard. The covered foaming composition is then passed into a double-belt press type apparatus where the curing exotherm continues to vaporize and expend the blowing agent, thereby forming the composition as it is cured. All the processes mentioned above lead to rigid phenolic foams exhibiting varying degrees of compressive strength properties. Therefore, the closed cell phenolic foams designed so far face two major problems. First, they are allowed to contain entrapped fluorocarbons for a somewhat higher insulation value but which are detrimental to the earth's atmosphere. Secondly, in many prior art phenolic foams, when cell walls are subjected to high temperatures or to external pressure, the cell walls cannot resist to these pressures and crack. Obviously, cracking of the cell walls allows the fluorocarbon blowing agents to leak out during curing or over time which consequently decreases the insulation properties of the product. Mendelsohn et al. and Smith, respectively in U.S. Patents 4,107,107 and 4,350,776, designed phenolic foams that could be used as high compressive strength, non-flammable materials while possessing low friability properties. In the case of U.S. Patent 4,107,107, the result was achieved by using a process requiring both a dual surfactant and a dual acid system. Still, the phenolic foam described in U.S. Patent 4,107,107 is a "rigid"foam system with or without entrapped fluorocarbons. In the case of U.S. Patent 4,350,776, the inventor used a furfuryl-alcohol polymer to obtain a low friability and flame resistant thermosetting foam. This foam is also a rigid phenolic foam product having entrapped therein suitable blowing agents such as fluorinated compounds. In both cases, however, the final product still has a rigid form and even though compression properties have been improved, the foam is still friable. Thus, substantially rigid phenolic foams have been known for many years. The rigidity and friability of these foams and the inherent lack of elastic deformation characteristics are such that these foams can be easily damaged when handled or when they are submitted to any type of external pressure. Most of these foams become more friable over time. As a result, these foams cannot be utilized in many applications where their good insulating and fire resistant properties would otherwise make their use preferable. Such applications include cushioning and insulation where flexibility and elasticity are required to reduce damage that could occur by friction fitting, impact, loading or lifting. In these applications, the known rigid phenolic foams crush under load and remain permanently deformed. Consequently, although the rigid close cell or substantially close cell phenolic foams containing entrapped fluorocarbon blowing agents have excellent insulation properties, their use has been found to be fairly limited. In the case of open cell phenolic foams, it was thought for a long time that these foams were to be used only in conditions where easy friability of the product was desired. For example, Smithers in U.S. Patent 2,753,277 describes a material employed for floral supporting means, the material being made of a phenol-formaldehyde foam to which a foaming agent and a catalyst are added. Similar products are described in U.S. Patent 3,049,444 issued to A.M. Palombo who disclosed a cellular synthetic material impregnated with a wetting agent. The synthetic material is a phenol-formaldehyde foam. In these documents as well as in other U.S. Patent documents such as U.S. Patents 3,287,104, 3,697,457 and 4,225,679, phenolic resoles are mixed with a surfactant, a wetting agent, a dye and a blowing agent. The resulting mixture is then reacted with a catalyst, usually an acidic catalyst and allowed to expand and cure to a rigid, hard and highly friable foam, capable of absorbing water and allowing the flower stems to enter the wet foam by applying only a slight pressure. Thus, none of the open or close cell phenolic foams disclosed in the prior art possess the desired flexibility property. Furthermore, in both cases, it seemed so far to have been impossible to obtain suitable stable flexibility of the foam while maintaining acceptable insulating and fire resistant properties. In accordance with the present invention, there is provided a semi-flexible or flexible phenolic foam composition having a substantially open cellular structure. This composition comprises the reaction product of a mixture of 100 parts by weight of a phenol-aldehyde resin, between 0.5 and 20 parts by weight of a surfactant, from 1 to 20 parts by weight of a blowing agent, optionally between 0 and 10 parts by weight of a wetting agent and from 5 to 20 parts by weight of a an acid catalyst. Hereinafter the proportions of all the ingredients entering in the composition are based on 100 parts by weight of resin unless otherwise specified. Also within the scope of the present invention is a method for producing a semi-flexible or flexible phenolic foam composition having a substantially open cellular structure. The method comprises: a) mixing a phenol-aldehyde resin with a surfactant, a blowing agent and optionally a wetting agent; b) curing said mixture by reacting same with an amount of acid catalyst sufficient to initiate curing; and c) compressing the cured or semi-cured product below its original thickness and releasing the pressure, thereby obtaining the desired semi-flexible or flexible phenolic foam composition. The flexible phenolic foam thereby obtained is not only an excellent insulation material which can be used to replace glass and mineral wool insulation, but also exhibits the excellent fire and smoke resistance properties inherent to phenolic foams. Even though the insulation properties of the semi-flexible or flexible, open cell phenolic foams are lower than those of the closed cell phenolic foams which contain trapped fluorocarbons, it is to be noted that the insulating properties of the semi-flexible or flexible foams are initially only about 30% lower than the insulating properties of the closed cell phenolic foams. Upon aging, the open, perforated but semi-flexible or flexible foam retains its initial insulation value depending mainly on the trapped air. However, the environmental problems associated with the use of the fluorocarbons make the use of the semi-flexible or flexible foams of the present invention particularly desirable. Furthermore, semi-flexible or flexible phenolic foams having almost half the density of the closed cell foams can have about 70% of the initial insulation properties of the closed cell foams. Thus, the main advantages of the semi-flexible phenolic foams of the present invention is that they possess a lower density which makes them economical and easy to handle. Furthermore, they can be friction fitted, easily cut and packed and used for purposes where other rigid and friable foams could not be used. The obtaining of a semi-flexible or flexible phenolic foam is a clearly unexpected result sine nowhere in the prior art is it disclosed or suggested that the preparation of stable elastic phenolic foams is forseeable or possible. In the accompanying drawings Figures 1 to 3 show the microstructure of a preferred flexible phenolic foam according to the invention seen through scanning electron microscopy; respectively in top, side and bottom view in Fig. 1, 2 and 3. To make the stable semiflexible or flexible phenolic foam composition of the invention, there is first prepared a phenolic resin constituted of a suitable phenolic resol, novolak or a mixture of a phenolic resol and a novolak. This phenolic resin is mixed with surfactants, an optional wetting agent which is also acting as a cell opener, a blowing agent or a mixture of blowing agents, desired dye or colouring agents, an acid catalyst and optionally compounds capable of improving both the fire and smoke resistance properties of the foam, such as borates, phosphates and certain nitrogenous compounds such as amines. The ingredients are mixed together with a high speed, high shear mixer to form a totally homogeneous mixture which has after curing and initial deformation a fine but spongy and semi-flexible to almost flexible foam structure. Once the cured foam has been obtained, it is subjected to deformation by being compressed below its original thickness, preferably by being compressed to between 5 and 60% of its original thickness for a period of time of at least 2 seconds. Once compression is released, the foam regains up to 95% of its original thickness and maintains its semi-flexible or flexible state permanently. This further step of compressing the cut foam slabs or sheets can be done from at least one direction in a squeeze motion during or after the foam has cured in a stationary or continuous production process. The foam nay be used thus or neutralized with a gas such as ammonia and washed to neutralize the residual acidity. The various components of the semi-flexible or flexible phenolic foam material of the invention will be described in further detail. Phenolic resin The phenolic resing that can be used are referred to as "phenol-aldehyde resins", and generally contain one phenol and one aldehyde component. Two general types of phenolic resins that are well known in the art are the novolaks and the resols. Novolaks Novolaks are usually prepared by reacting excess amounts of phenol with formaldehyde. The novolak resin molecule is built up from dihydroxyphenylmethane which upon further addition of formaldehyde and immediate condensation of alcohol groups thus formed with another phenol molecule gives linear compounds having the general formula H(C 6 H 3 (OH).CH 2 )n C 6 H 4 .OH as well as branched polymers in which some of the benzene rings have three methylene bridge attachments under acidic conditions. Novolaks can also be made under alkaline conditions and both types of novolaks can be incorporated into a resol, made separately or in-situ for the purpose of producing phenolic foams. Resols As a general rule, liquid resol resins are prepared by reacting one or more phenols with an excess of one or more aldehydes in aqueous phase and in the presence of an alkaline catalyst. The excess of aldehyde may be small or large, depending on the type of resin required to produce the desired flexible or semi-flexible phenolic foam of the present invention. The chemistry of the phenolic novolaks and resols is well known to those skilled in the art. Phenol The term "phenol" can include not only phenol itself (including pure and technical grade phenol) but also other phenol compounds such as resorcinol, cresol, xylenol, chlorophenol, bisphenol-A, α-naphthol and β-naphthol, and admixtures thereof. Aldehydes Aldehydes to be used for reaction with the above mentioned phenols usually contain 1 to 8 carbon atoms and preferably 1 to 3 carbon atoms. Specific examples of aldehydes include formaldehyde, acetaldehyde, propionic aldehyde, furfural and benzaldehyde and admixtures thereof. In the present invention, the use of formaldehyde is preferred. The most common commercially available forms of formaldehyde include formalin, which is usually a 30-52% by weight aqueous solution of formaldehyde in water; paraformaldehyde, which is a solid linear polymer of formaldehyde; and trioxane, which is a solid cyclic tripolymer of formaldehyde. The above and other sources of formaldehyde for reaction with phenol are intended to be embraced herein by the term "formaldehyde". In order to achieve maximum flexibility in preparing the phenolic foams of the present invention, it is required that the phenolic resol or the mixture of resols or resols and novolaks that will be used have a phenol-to-formaldehyde ratio in a range that will readily allow a proper cure time. Preferably, the phenol-to-formaldehyde ratio is between 1.0 to 2.0 and more preferably a ratio of 1.0 to 1.6 has been found to be the most suitable. Surfactant The surfactant may be selected from any suitable stabilizing agent useful in stabilizing liquid phenol-aldehyde resin foams. The surfactant can be anionic, cationic, non-ionic or amphoteric. The only restriction of any significance is the obvious one that it must not interfere with the foaming process. A large number of suitable surfactants are known and are disclosed in numerous publications. In general, the preferred stabilizing agents are water-soluble and acid -stable surface active agents, and for best results they are also non-hydrolyzable. Commonly used surfactants include silicon surfactants such as siloxane-oxyalkylene copolymers and organic surfactants such as polyethers and polyalcohols, including their condensation products and alkylene oxides such as ethylene oxides and propylene oxides, with alkyl phenols, fatty acids, alkylsilanes and silicons. Specific examples include polyoxyethylene octadecylphenol, polyoxyethylene decylphenol sulphate, polyoxyethylene dodecyl phenol, polyoxyethylene octyl phenol, polyoxyethylene linoleic acid ester, polyoxyethylene stearic acid ester, polyoxyethylene sorbitan monolaurate and polyoxyethylene sorbitan tristearate Preferably, for the purposes of the present invention, specific commercially available surfactants are useful. These surfactants include the copolymers manufactured by the Dow Corning Corporation under the trade name "DC- 193" as well as the Tween™ series of surfactants marketed by ICI Americas Inc.. The type and the percentage of surfactant to be used in the present invention should be properly assessed. A proper surfactant will yield finer cell structure and thinner cell walls which will promote and favour better flexibility of the final product. The amount of surfactant used will usually be higher than 1% by weight of the phenolic resin. It has been found that a surfactant amount of between 2 and 10% by weight of the phenol-aldehyde resin yields the best results. It is to be noted that higher surfactant levels seem to yield foams having a fine cell structure, thereby enhancing flexibility of the final product. Wetting agent The use of a wetting agent in the present invention is optional although it usually increases the flexibility of the resulting foam and leaves the cell walls open to release vapor, and dry quickly, and at lower surfactant levels and to allow easier initial deformation. At lower surfactant levels and in the case of inadequate mixing, the use of wetting agents or cell openers becomes essential whereas high levels of surfactant do not usually necessitate the use of a wetting agent. Various types of agents which reduce surface tension may be employed for the purposes of the present invention, including alcohols, glycols, sorbitol and glycerol,with sodium lauryl ether sulfate or ammonium lauryl ether sulfate being preferred. A useful guide in selecting the most suited surfactant and wetting agent is the HLB (Hydrophile-Lipophile Balance) number system developed by ICI Americas Inc. Blowing agents Typical blowing agents which may be employed in preparing the flexible phenolic foam of the present invention include physical and chemical blowing agents as well as mechanical blowing techniques. However, the preferred blowing agent and technique comprise the employment of liquid physical blowing agents, the agents which are volatile liquids introduced into the reaction mixture, and which produce a blowing gas through vaporization of the blowing agent or through decomposition of the blowing agent during the exotherm. Numerous blowing agents suitable for use in the present invention are well known in the prior art. Ideally, the blowing agent should be a liquid having an atmospheric pressure boiling point between -50 and 100°C and more preferably between 0 and 50°C. In fact, any compound capable of reaching a gaseous state during curing or capable of generating a gas can be used in the present invention. Examples of volatile blowing agents include organic compounds such as hydrocarbons, halogenated hydrocarbons, alcohols, ketones and ethers, normally gaseous elemental substances and normally gaseous inorganic compounds. Specific examples of hydrocarbon blowing agents include methane, ethane, propane, butane, octane, isobutane, cyclobutane, pentane, cyclopentane, isopentane, hexane and the corresponding unsaturated derivatives thereof which contain one or more carbon-to-carbon double bonds. Other suitable blowing agents include chlorinated and fluorinated hydrocarbons such as chloroform, trichlorofluoromethane, 1,1,2-trichloro-1,2,2-trichlorofluoroethane, ditrifluoromethane, 1,2-difluoroethane and 1,1,1,2-tetrachloro-2,2-difluoroethane. Many other blowing agents known in the art can be employed in the present invention, although the use of fluorinated blowing agents is not favored because of environmental considerations. Mixtures of one or more blowing agents, e.g. liquid-liquid, or liquid-gas, can be used. Azeotropes of blowing agent mixtures are often used. Preferably, a mixture containing 25% n-hexane and 75% n-pentane is used in the present invention. These flammable blowing agents can be replaced partially or completely by non-flammable blowing agents such as CFC's (chloro-fluorocarbons) or their environmentally safer varieties. Finally air or liquid air as well as mixtures of gases can also be employed as suitable blowing agents. The blowing agents are employed in an amount sufficient to give the resulting foam the desired bulk density. In the case of the present invention, the required amount of blowing agent will depend on the density of the final product but will usually be between 5 and 15, preferably between 10 and 15 parts per 100 parts by weight of the phenol-aldehyde resin. The catalysts The catalysts also have a considerable influence on the final flexibility of the semi-flexible or flexible phenolic foam of the present invention. Also, plasticizers added into either the resin mixture or the plasticizing catalysts help to increase the flexibility of the final product. The catalyst may generally be chosen from a wide variety of strong organic acids such as oxalic acid, maleic acid, maleic anhydride, hydrochloric acid and sulphuric acid. Also, the catalysts may be selected from aromatic sulphonic acids such as phenol sulphonic acid, benzene sulphonic acid, toluene sulphonic acid and xylene sulphonic acid (many mixtures of such acids can be used). A particularly preferred catalyst is a mixture containing about 15 parts by weight of 85% phosphoric acid, about 15 parts by wt. 70% methane sulphonic acid and about 70 parts by weight of 65% phenol sulphonic acid. In most instances, the acid catalyst is added in amounts sufficient to reduce the initial pH of the liquid resin mixture below 5, preferably between 1.5 and 3.0. Also, the amount of catalyst needed can be determined by evaluating the desired cream times and firm times of the reaction mixture. Generally, however, the concentration of catalyst contained in the foaming reaction mixture will vary between 5 and 20, and preferably in the range 8-15 when the preferred phosphoric acid-methane sulphonic acid-phenol sulphonic acid catalyst described above is used. Procedure for the preparation of the flexible phenolic foams Generally, the first step involved in preparing the semi-flexible or flexible phenolic foams of the present invention comprises mixing the phenol-aldehyde resin with the surfactant, the blowing agent and optionally the wetting agent. Preferably, this first step of the process comprises mixing 100 parts by weight of the phenol-aldehyde resin with between 0.5 and 20 parts by weight of the surfactant, from 1 to 20 parts by weight of a blowing agent and optionally between 0 or 0.5 and 10 parts by weight of a wetting or cell opening agent. More preferably, the first step of the process comprises mixing 100 parts by weight of the phenol-aldehyde resin with from 5 to 8 parts by weight of a surfactant, 8 to 10 parts by weight of a blowing agent and 2.5 to 4.0 parts by weight of a wetting agent. The resulting formulation can be mixed using a paint grinder type high speed high sheer mixer until a fully homogenized mixture is obtained. This first mixture is to be referred to as the "resin mixture". In a separate container, a "catalyst mixture" is prepared. This "catalyst mixture" can contain various amounts of selected catalysts but it has been found that catalyst mixtures containing between 60 and 65 parts by weight of phenol sulphonic acid 65%, between 15 and 20 parts by weight of methane sulphonic acid 70% and from 15 to 25 parts by weight of phosphoric acid 85% are particularly suited for the present invention. The various ingredients of the "catalyst mixture" are to be mixed to homogeneity and stabilized at room temperature. Once the desired "resin mixture" and "catalyst mixture" have been obtained, the "resin mixture" is cured by pouring it into a mixing container to which the "catalyst mixture" is added in amounts sufficient to initiate curing. Preferably, between 15 and 20 parts by weight of "catalyst mixture" will be added to 100 parts by weight of the resin mixture. The materials are then mixed at high speed for a time sufficient for the ingredients to be properly mixed prior to foaming. The required time will usually range between 30 and 120 seconds. Once the mixture has been thoroughly homogenized, it should be poured into a mold of low heat conductibility such as a wooden mold previously heated at a temperature of from room temperature to approximately 65°C in order to avoid heat sink and extra foam skin. The mold and the poured foam is then kept in an atmosphere at a temperature ranging between room temperature and 65°C in order to allow the foam to cure. The curing time will usually be between half an hour and 24 hours. Once the foam has been properly cured, it should be allowed to stand at room temperature for a period of from 2 to 24 hours before cutting and deforming steps are undertaken after the foam has cooled. Once the foam has been cured and preferably has reached room temperature, it can be cut to the desired thickness. Although at this stage the foam already exhibits some flexibility, it is then subjected to an additional deformation step that will definitely ensure semi-flexibility or flexibility of the final product. Thus, a foam sheet may be placed between two rigid plates and uniform pressure is to be applied to compress the foam sheet below its original thickness. Preferably, the sheet should be compressed to 5 to 60%, more preferably 50 to 60% of its original thickness. The pressure should be held for a period of time sufficient to ensure permanent flexibility or semi-flexibility of the foam upon release. Preferably, the compression time is at least 2 seconds, more preferably from 2 to 60 seconds and still more preferably about 10 seconds, after which the pressure is released. Then the phenolic foam will regain approximately 50 to 95% of its original thickness and will remain permanently deformed and semi-flexible or flexible. The deformation step described above is essential to coil the cells which will remain permanently deformed and flexible. The above-noted process can be fully automated through already available automatic proportioning, mixing, foam lay-down, curing, cutting and deformation equipment used for other foam systems. With only minor modifications, existing manufacturing units can be adapted to produce the flexible phenolic foams of the present invention. Therefore, the composition of the present invention can be produced via the manual single pour, multiple pour, continuous bun process or via the multiple component manual or automated dispensing machines in combination with continuous slab sheet production techniques. The following example illustrates the invention. Example 1 Preparation of a flexible phenol-formaldehyde foam A. Preparation of a phenol-formaldehyde resin. In a glass reaction vessel equipped with a stirrer, condenser, thermometer and vacuum distillation equipment were loaded 940 grams of phenol and 840 grams of 50% aqueous formaldehyde. After the reaction mixture had been cooled to a temperature ranging between 40 and 45°C, 25% aqueous sodium hydroxide was added in sufficient amounts to adjust the pH of the reaction mixture to a value ranging between 8.7 and 8.8. The mixture was then heated under constant mixing to a temperature in the range of 50 to 52°C and allowed via exothermic reaction to reach atmospheric reflux at 100-103°C at sea level. The atmospheric reflux was continued until over 95% of the formaldehyde was reacted and until a batch sample, when cooled to 30-35°C, showed turbidity. The reaction mixture was then cooled to 50-55°C and neutralized with concentrated formic acid to a pH value of 7.2-7.4. The resulting resol was then vacuum distilled to a viscosity of 4,000-5,000 centipoise at 25°C without letting the reaction temperature exceed 60°C. The resulting resin was cooled and stored in a refrigerated storage area. B. Preparation of a flexible phenol-formaldehyde foam. 1° Preparation of the resin mixture. 100 parts by weight of the phenolic resin obtained in A. were mixed with 4 parts by weight of the surfactant sold by ICI Americas Inc. under the trade name G-1292, two parts by weight of the surfactant marketed by Dow Corning Corporation under the trade name DC-193, two parts by weight of the wetting or cell opening agent marketed by Alcolac under the trade name L-22 and 15 parts by weight of a blowing agent containing 75% n-pentane and 25% n-hexane. All the ingredients were mixed together for 1 minute using high speed high shear mixing until the mixture had completely homogenized. The temperature of the mixture was maintained at 20°C. 2° Preparation of the catalyst mixture. 70 parts by weight of 65% phenol sulphonic acid, 15% parts by weight of 70% methane sulphonic acid and 15% by weight of 85% phosphoric acid were mixed together and the mixture was stabilized at a temperature ranging between 20 and 25°C. 3° Preparation of the flexible phenolic foam. 85 parts of the resin mixture prepared in 1° were poured in a mixing container and 15 parts of the catalyst mixture prepared in 2° were added. The materials were mixed together at 3000 rpm for a time sufficient to properly mix the ingredients prior to foaming. The resulting mixture was' poured into a wooden box mold preheated to 45°C and the mixture was allowed to freely rise. Once the mixture was raised the mold was maintained at a temperature of between 45 and 50°C in order to allow the foam to cure for a period of about 2 hours. After curing, the foam was allowed to stand at room temperature for 24 hours. Once the foam has thoroughly cured, it is cut to the required thickness. At this stage, the foam is already semi-flexible but it must be subjected to a deformation step before being flexible. A 25 mm thick foam sheet was placed between two steel plates and uniform pressure was applied to squeeze the 25 mm foam to a deformation thickness of 15 mm. The pressure was held for 10 seconds and then released. The foam regained about 5 mm of its thickness reaching a final stable thickness of 20 mm. Thus, the foam regained 80% of its original thickness and remained permanently flexible. Table 1 shows some of the properties of the flexible phenolic foam of the present invention when compared with a rigid closed cell phenolic foam. PRODUCT FLEXIBLE PHENOLIC FOAM RIGID-CLOSED CELL PHENOLIC FOAM Density (Pounds/Cu.Ft.) 1.0-1.5 2.0-3.0 kg/m 3 16-24 32-48 k. factor (BTU/inch/hour/foot 2 /°F) 0.22-0.24 0.13-0.15 w/m K 0,031-0,035 0,018-0,022 Table 2 illustrates other properties of the flexible phenolic foam of the present invention when compared to the flexible polyurethane foams. PHYSICAL PROPERTIES FLEXIBLE PHENOLIC FOAM FLEXIBLE POLYURETHANE Density(pcf) 1.0 1.0 Cell Structure open open Orientation (direction) X Z Z Compressive Strength at 25% Deformation (kpa) 1.65 5.4 4.4 Tensile Strength (kpa) 33.0 12.0 80.0 The flexible foam obtained in Example 1 was subjected to cyclic compressive tests and the results are listed in Table 3. Finally, the flexible phenolic foam of the present invention was subjected to dimensional stability tests and the results are given in Table 4. Sample Conditioning %Change Length Width Thickness Weight Density Heat Aging (80°C for 7 days) -0.5 -0.8 +0.9 -7.4 -6.7 Heat and Humid Aging (70°C, 90% Relative Humidity for 7 days) 0 +0.2 +5.1 -3.3 -8.6

Claims: A foamed phenolic resin sheet material prepared from a phenol-aldehyde resin, a surfactant and a blowing agent, characterised in that it is the reaction product of, by weight, 100 parts of said resin, 0.5 to 20 parts of surfactant, 1 to 20 parts of blowing agent, 5 to 20 parts of an acid catalyst, and optionally up to 10 parts of a wetting agent, and has been compressed to have a thickness of 5 to 60% of its original thickness for a period of time sufficiently to coil the cells of the foam permanently upon release whereafter it remains permanently deformed, and is flexible or semi-flexible and has a substantially open cellular structure. A process for producing a foamed phenolic resin sheet material which comprises mixing a liquid phenol-aldehyde resin, a blowing agent, a surfactant and an acid catalyst as curing agent and optionally other additives and allowing reaction and foaming to form a cellular structure, characterised in that the cured or semicured product is compressed to between 5 and 60% of its original thickness for a period of time sufficiently to coil the cells of the foam permanently upon release and the pressure then released, whereupon the foam remains permanently deformed and a semi-flexible or flexible product is obtained. A process as claimed in Claim 2, wherein the sheet of the cured product regains 50 to 95% of its original thickness after release of the pressure. A process as claimed in Claim 2 or 3, wherein the cured product is compressed for a period of 2 to 60 seconds. A process as claimed in Claim 4, wherein the compression is for from 2 to 10 seconds. A process as claimed in Claim 5, wherein the compression is for 10 seconds, to from 50 to 60% of the original sheet thickness. A process as claimed in any of Claims 2 to 6, wherein the mixture to be reacted includes a wetting agent as cell opening agent. A process as claimed in Claim 7, wherein there is mixed together, in parts by weight, 100 parts of the resin, 0.5 to 20 parts of surfactant, 1 to 20 parts of blowing agent and 1 to 10 parts of wetting agent. A process claimed in Claim 8, wherein there is mixed, per 100 parts of the resin, 5 to 8 parts of surfactant, 8 to 10 parts of blowing agent and 2.5 to 4 parts of wetting agent, and 100 parts of the mixture is mixed with 15 to 20 parts of acid catalyst. A process as claimed in any of Claims 2 to 9, wherein the catalyst is a mixture, in parts by weight, of 60 to 65 parts of 65% phenol sulphonic acid, 15 to 20 parts of 70% methane sulphonic acid and 15 to 25 parts of 85% phosphoric acid. A process or material as claimed in any preceding claim, wherein the phenol-aldehyde resin or mixture of resins used has a ratio of phenol to formaldehyde of between 1.0 and 2.0. A process or material as claimed in any preceding claim, wherein the phenol component of the phenol-aldehyde resin is phenol, resorcinol, cresol, xylenol, chlorophenol, bisphenol-A, alpha-naphthol or beta-naphthol. A process or material as claimed in any preceeding claim, wherein there is incorporated into the foam a substance capable of improving the resistance of the foam to fire and smoke.

Inventors: SUDAN KRISHAN K, SUDAN, KRISHAN K.
Applicants: STELLARTECH AFRICA PROPRIETARY, STELLARTECH AFRICA (PROPRIETARY) LIMITED
Application year: 1990
Main classification: C08J9
IPC codes: C08J9, C08L61