WO2004013215A1

WO2004013215A1 - Water absorbent flexible polyurethane foam

Info

Publication number: WO2004013215A1
Application number: PCT/AU2003/000929
Authority: WO
Inventors: Zoica Sterjova; Rob Sack
Original assignee: Pacific Brands Household Products Pty Ltd
Priority date: 2002-08-01
Filing date: 2003-07-22
Publication date: 2004-02-12
Also published as: AU2002950525A0

Abstract

A process of preparing an open cell hydrophilic foam comprising the steps of reacting in a single step, a reaction mixture to produce an open cell hydrophilic polyurethane foam and reducing the volume of the foam to 5-70% of the original volume. The reaction mixture comprises an organic polyisocyanate, water, a reaction catalyst and a polyol component including a poly(oxyalkylene) polyol having an ethylene oxide content of at least 50%.

Description

WATER ABSORBENT FLEXIBLE POLYURETHANE FOAM Technical Field

This invention relates to flexible polyurethane foams and in particular to such foams that are water absorbent. The invention also relates to methods of preparing such foams and articles prepared with and from such foams.

Background of the Invention

Water absorbing foam materials have been widely available for many years and have been used for floor mops, kitchen wipes and other similar applications. Highly water absorbent foams have been generally used for removing water from surfaces. The gas phase in a cellular polymer is usually distributed in voids or pockets called cells. If the cells are interconnected in such a manner that gas can pass from one to another, the material is termed open-celled. If the cells are discrete and the gas phase of each cell is independent of that of the other cells, the material is termed closed celled. In water absorption applications these foamed materials are open celled and usually cellulose derived. However, cellulose sponges are deficient in a number of areas. Being a natural product, cellulose is a food source for bacteria and quickly begins to break down causing loss of strength and emission of a foul odour. Dirt also stains the cellulose giving it a grubby appearance. When cellulose dries out, it becomes stiff and brittle and can crack. The sponge must be wet out before use. Hence, cellulose has a short life span.

Typically a cellulose derived sponge is manufactured from a mixture of viscose, reinforcing fibres such as cotton fibres or hemp fibres, a cell-forming agent and salt cake. It is desirable for such sponges to have good flexibility in a dry state. However, such sponges generally do not exhibit good dry flexibility. Attempts to improve the dry flexibility by including plasticisers such as glycerol or propylene glycol have not been satisfactory. Cellulose-derived sponges impregnated with such plasticisers exhibit good softness but once washed with water the sponge exhibits poor softness after being dried as the plasticiser has been leached away.

As well as cellulose-derived foams other materials have been used for foams. These include polyvinyl alcohol (PVA) foams and polyurethane foams. PVA foams suffer from a similar problem to cellulose derived foams in that when dried they are no longer flexible.

Polyurethane foams are another type of foamed material. These polymers were first formed in the 1930's by addition polymerisation of diisocyanates with polyols. These days, the general chemical ingredients of a polyurethane foam system are a polyfunctional isocyanate and a hydroxyl- containing polymer, along with the catalysts necessary to control the rate and type of reaction and other additives to control the surface chemistry of the process.

The most common types of blowing agents for urethane foams are water or volatile fluids such as halocarbons. While water is called the blowing agent, in fact it is carbon dioxide that acts as the blowing agent, as it is generated in situ by the reaction of isocyanate with water. When liquid halocarbons are utilised, they evaporate to produce a gas as the foaming mixture heats up.

The general method of producing a cellular polyurethane is to mix the polyfunctional isocyanate, hydroxyl containing polymer, catalysts, blowing agents and other additives and adjust process conditions and ratios of the reactants such that the heat from the reaction causes evaporation of the blowing agent resulting in the creation of a foam. The stabilisation of the polymer, generally by cross-linking, is timed to coincide at the time corresponding to minimum density of the resultant foam.

The resulting polyurethane foams can vary broadly in molecular weight and physical properties depending on the degree of cross-linking as well as the structure of the foam. The average molecular weight between cross-links is generally 2,500-25,000 for flexible polyurethane foams. Commercially, polyurethane foams are generally produced utilising one of two fundamentally different methods, generally known as the "one-shot" method and the "prepolymer" or "two-shot" method.

In the late 1950's, it was discovered that foam could be manufactured directly from the chemical components using newly developed surfactants and catalysts (One shot process). In a one-shot process all the polyurethane foam ingredients are mixed and then discharged from the mixer to form the foam. The reactions begin immediately and proceed at such a rate that expansion starts quickly, usually in less than 10 seconds. The expansion generally takes a few minutes. Curing may continue for several days. However due to the nature of the chemistry (high EO content required for hydrophilic foam) foam manufacturers have generally not used this process for manufacturing hydrophilic foam.

Traditionally, hydrophilic foam has been made in a two-shot process utilising the prepolymer intermediate step.

In the two-step or prepolymer process the polyhydroxy component is reacted with an excess amount of polyisocyanate sufficient to form a prepolymer with isocyanate end groups. The prepolymer mixture is then reacted with a resin blend, which may include a blowing agent such as water or organic blowing agents. When water is utilised as the blowing agent, reaction of the water with the prepolymer causes the release of carbon dioxide for expansion of the foam.

Environmental concerns dictate that polyurethane foams be made without the use of significant amounts of volatile organic blowing agents that are damaging to the environment, such as CFCs. Hence, there is a need to produce a hydrophilic foam without the use of volatile organic blowing agents.

Water absorbing flexible polyurethane foams are disclosed in US Patent 6,034,149. The foams are prepared by reacting on isocyanate terminated prepolymer where the prepolymer has a oxyethylene content of at least 50% by weight with water. The process is thus a "two shot" process as described above.

The foamed compositions of this citation preferably include super absorbent polymers (SAP). The foam slabs are compressed after formation to at most 60% of the thickness of the foam slab before compression. The compression is conducted for extended times and at elevated temperatures.

Environmental concerns dictate that polyurethane foams be made without the use of significant amounts of volatile organic blowing agents that are damaging to the environment, such as CFCs. Hence, there is a need to produce a hydrophilic foam without the use of volatile organic blowing agents. Summary of the Invention

This invention provides in one form a process of preparing an open cell hydrophilic foam comprising the steps of: reacting in a single step, a reaction mixture to produce an open cell hydrophilic polyurethane foam, the reaction mixture comprising an organic polyisocyanate, water, a reaction catalyst and a polyol component including a poly(oxyalkylene) polyol having an ethylene oxide content of at least 50%; and reducing the volume of the foam to 5-70% of the original volume.

In one preferred form of the invention, the reaction mixture further includes a thermosetting agent and the ethylene oxide content of the polyol component preferably in the range of 60-90%. The step of reducing the volume of the foam may be accomplished by physically compressing the expanded foam and exposing a particle to an elevated temperature. As mentioned above, the temperature employed is generally in the range of 100-220°C, and heated plates or an oven may be used to increase the temperature. Where the article is compressed by physical means, this step preferably occurs shortly after reaction so that the core temperature remains sufficiently high to achieve permanent compression as a consequence of the exothermic reaction has taken place. The physical compression step may be followed by removal of the compression device with the compression time dependent on the thickness of the article and the temperature of compression. These compressing devices can be removed immediately after compression or after the foam returns to ambient temperature.

In another form of the invention, the volume reducing step may be accomplished by expansion of the reacting chemicals taking place at a pressure greater than atmospheric. Alternatively, the volume reducing step may be accomplished by chemically compressing the free rise expanded foam by reducing/increasing the amounts of a chemical component in the formulation. A person skilled in the art of making polyurethane foam can achieve chemical compression (semi collapse/collapse in polyurethane foam by reducing the stability of the foam. For example, a decrease in silicone, cross-linkers, tin catalyst or an increase in blowing agent (water, amine, others) to the degree where the cells would coalesce and lead to foam instability. The core temperature of the foam remains sufficiently high because of the exothermic reaction that has taken place to achieve permanent compression.

In another form of the invention, the volume reducing step may be accomplished by overpacking in a mould. The core temperature of the foam remains sufficiently high because of the exothermic reaction that has taken place to achieve permanent compression.

The invention also provides, an open cell, hydrophilic polyurethane foam which may be formed by the above process. The invention further provides a open cell, hydrophilic polyurethane foam having at least one of the following characteristics. a) Fluid Capacity (FC) greater than 0.9 g/cm³; b) Wet Capacity (WC) greater than 0.95 ; c) Equilibrium Moisture (EM) of approximately 40-60%; d) Surface Drying (SD) of greater than 50%; e) Capillary Action (CA) higher than 20mm; and . f) Cell count (CC) of at least 8,000.

In a preferred form of the invention, the foam has all of the above characteristics. Furthermore, the surface drying (SD) may be greater than 80% and may even be as high as 95%. The capillary action is preferably greater than 30mm and preferably higher than 40mm. While the cell count (CC) is greater than 40, 000 in the preferred form, and greater than 80, 000 in the most preferred form. Other characteristics which are desirably possessed by the open cell hydrophilic polyurethane foam of the present invention are a dripping tendency (DT) less than 35%, a percentage equilibrium swelling (ES) of less than 100% but more preferably less than 75% and less than 50% in the most preferred form. Other preferred characteristics of the open call hydrophilic polyurethane foam of the present invention are a percentage dry swelling (DS) of less than 100%, preferably less than 75% and less than 50% in the most preferred form and a release factor (RF) greater than 70%.

The tests for determining each of these characteristics are described later in the specification. Detailed Description of the Invention

The general chemical components of a one-shot polyurethane foam system are a polyfunctional isocyanate and polyfunctional alcohol, along with the catalysts necessary to control the rate and type of reaction and other additives to control the surface chemistry of the process. The general method of producing cellular polyurethane is to mix the polyfunctional isocyanate, polyfunctional alcohols, catalysts, blowing agents and other additives. Carbon dioxide generated in situ by the reaction of isocyanate with water acts as a blowing agent and the heat from the reaction causes evaporation of volatile- blowing agent resulting in the creation of foam. In a one-shot process all the polyurethane foam ingredients are mixed and then discharged from the mixer to form the foam. The reactions begin immediately and proceed at such a rate that expansion starts quickly, usually in less than 10 seconds. The expansion generally takes a few minutes. Curing may continue for several days.

Suitable polyfunctional isocyanates are any that when utilised in the process of the present invention will yield the desired open cell, hydrophilic polyurethane foam. Examples of suitable organic polyisocyanates include toluene diisocyanate, such as the 80:20 mixture or the 65:35 mixture of the 2,4- and 2,6-isomers, ethylene diisocyanate, propylene diisocyanate, methylene-bis- 4-phenyl isocyanate, 3,3'bis-toluene-4,4'-diisocyanate, hexamethylene diisocyanate, napthalene-l,5-diisocyanate polymethylene polyphenylene diisocyanate, mixtures thereof and the like. The preferred organic polyisocyanate is Toluene Diisocyanate (TDI 80/20). The amount of polyisocyanate employed in the present invention is any amount suitable to obtain the desired open cell, hydrophilic polyurethane foam. Generally, the amount of polyisocyanate employed in the process of this invention should be sufficient to provide at least about 0.5 NCO equivalent per hydroxyl group present in the reaction system (that is, isocyanate index of 50), which includes all the polyol reactants including water. It is preferable to employ sufficient isocyanate to provide an isocyanate index not greater than about 115, preferably in the range of about 50 and about 100.

The term 'polyol' is an abbreviated name for poly-functional alcohols. The are two main types of polyols that are utilised in the polyurethane industry, namely polyether polyols and polyester polyols. Polyether polyols are of particular importance to the invention. A polyether polyol chemically is a polyfunctional alcohol having a polymeric chain with ether (C-O-C) linkages. Polyol is a source of hydroxyl and other isocyanate reactive groups. It is the reaction of polyol with isocyanate that forms one of the fundamental reactions (gelling) in foam making. In flexible foam formulations polyether polyols are used, and based on the starting polyol structure, different processing and foam properties can be achieved.

Polyether polyols are made by reaction of an organic oxide with an initiator compound containing two or more active hydrogens. The active hydrogen compound, in the presence of a base catalyst, initiates ring opening and oxide addition, which is continued until the desired molecular weight is achieved. This is an exothermic reaction. If the initiator is a diol then a polyol with a functionality of two is obtained, a triol gives a functionality of 3 and so on. (Functionality is defined as the average number of isocyanate reactive groups in the given polyol.) However, trace amounts of water and allyl alcohol are present in the reaction mixture and act as co-initiators to produce some monol and diol and so the overall functionality of a polyol made using a triol initiator is somewhere between 2 and 3. The most common initiators used in the industry are triols.

Common oxides include Ethylene oxide, Propylene oxide, 1,2-Butylene oxide and Epichlorohydrin. Of these oxides the most commonly used commercially are Ethylene oxide (EO) and Propylene oxide (PO). Polymerisation using PO produces secondary terminal hydroxyl groups while EO produces primary terminal hydroxyl groups. Primary hydroxyl groups are about 3 times more reactive than secondary hydroxyls. As a result, the amount of EO used, and its distribution within the polyol can control its reactivity. EO can be incorporated in to the polyol in a random manner (random polyol) or in a deliberate sequence (block polyol). The OH number of a polyol is defined as the number of OH groups available for reaction. OH number is not restricted to polyols, however, and many ingredients in a formulation have an OH number. It is obtained by wet chemistry methods and is expressed as the number of milligrams of potassium hydroxide equivalent to the hydroxyl content in one gram of the polyol. US Patent 3,457,203 describes a process for preparing hydrophilic urethane foams from polyether polyols containing relatively large proportions of EO substituents in their composition.

Polyols can be varied in several ways to give different foam properties. As the molecular weight of a polyol increases its reactivity will decrease. As functionality is increased, an increase in gel time will be observed. Graft copolymer polyols are another way of changing foam properties. Copolymer polyols are polyether polyols that have been 'filled' with other organic polymers to produce a higher viscosity, white to off- white fluid. These types of polyols improve hardness and aid in processing by improved cell opening. The filler polymer is produced by in situ polymerisation of monomers in a polyol base through step growth or free radical polymerisation. The two main types of Graft copolymer polyol are SAN and PHD. SAN is produced by free radical polymerisation of styrene-acrylonitrile mixtures while PHD copolymers are produced by the step growth polymerisation of diamine and TDI. PHD copolymers produce larger particle sizes and a broader size distribution than is achieved with SAN copolymers. However, the final molecular weight of PHD copolymers is lower than that of SAN copolymers. Polyols used in the production of conventional foam are usually random EO/PO polyols with a molecular weight of 3000-4000 and a functionality of between two and three. Polyols used in the production of high resilience foam are usually block

EO/PO polyols also with a functionality of between two and six and a molecular weight of 4500-6000 and are often end-capped with EO. This not only achieves an equivalent or better reactivity to that of conventional polyols it has the added benefit of increasing the TDI and water compatibility of the polyol, hence, a lower efficiency surfactant can be used.

The polyol utilised may be any polyol or mixture of polyols that is useful for making polyurethane foam. At least one polyol in the present invention is a poly(oxyalkylene) polyol having an ethylene oxide content of at least 50% and preferably 60-90% and having a molecular weight preferably in range 3000-10000; whilst having hydroxyl values in the range of about 30-40. These polyols generally have at least three hydroxyl groups in each polyol. Typically, at least 20%> of the polyol content should be said polyol. More typically, from about 50 to 100% of all the polyols used will be said polyol. Polyols having higher, lower or no ethylene oxide contents are within the scope of the present invention, as are polyols having higher and lower hydroxyl values such as, but not limited to those listed below or as is any polyol considered useful for the purpose of making polyurethane foam. These include: i) polyoxypropylene diols; ii) polyoxypropylene triols; iii) polyoxypropylene tetrols; iv) polyoxypropylene pentols; v) polyoxypropylene hexols;

vi) ethylene-oxide-capped diols, triols, tetrols, pentols or hexols; vii) random and block polymers of the above in which the polyol is made with both ethylene and propylene oxides. When the oxides are fed as a mixed feed, the products are termed hetero polyols; viii) graft or copolymer polyols, which contain stable dispersions of a solid particulate polymeric phase in the liquid polyol phase; and ix) cross linkers, which are typically short chain polyfunctional molecules added to increase load bearing or initial foam stability.

The polyols which may be employed in the present invention generally include polyols having an ethylene oxide content of around 75%, whilst having hydroxyl values in the range of about 30-40. However, polyols having higher and lower ethylene oxide contents are within the scope of the present invention, as are polyols having higher and lower hydroxyl values. The polyols may be random, block or graft polyols and include mixtures of such polyols. The polyols generally have at least three hydroxyl groups in each polyol. It is to be noted that not all of the polyol content used in the process of the present invention need necessarily be polyols with ethylene oxide content of around 75%, only that a proportion of the polyol content be. Typically, at least 20% of the polyol content should be ethylene oxide content of around 75%. More typically, from about 50 to 100% of all the polyols used will be with ethylene oxide content of around 75%. The polyol content that is not with ethylene oxide content of around 75% can be any polyol that is typically used for the manufacture of polyurethane foam, that may include conventional polyol, copolymer polyol and/or high resilience polyol or combination of polyols or any other polyol typically used in the manufacture of polyurethane foam.

Foam density is determined by the amount of blowing agents present in the formulation, which is indicated by the blow index, that is the equivalent number of parts of water per 100 parts of polyol. The most common types of blowing agents for urethane foams are water or volatile fluids such as halocarbons. Water generally will be utilised in the present invention in an amount sufficient to produce the desired polyurethane foam, an auxiliary blowing agent such as, but not limited to methylene chloride, methyl chloroform, acetone or carbon dioxide may be used to fine tune physical properties of the foam. While water is called the blowing agent, in fact it is carbon dioxide that acts as the blowing agent, as it is generated in situ by the reaction of isocyanate with water. When liquid halocarbons are utilised, they evaporate to produce a gas as the foaming mixture heats up. Water is generally employed in an amount in the range of about 1 to 25 parts water per 100 parts by weight of the di- and polyhydric components. Generally, water is utilised in the range of about 1 to about 15 parts water per 100 parts by weight of the di- and polyhydric components, preferably in range of 2 to 10 parts and more preferably in range of 3 to 5 parts water per 100 parts by weight of the di- and polyhydric components. In the preparation of the polyurethane foams of the invention, minor amounts of one or more surfactants may be utilised to further improve the cell structure of the polyurethane foam. Silicones are primarily used as active agents or surfactants in the production of polyurethane foams. Their basic function is to: lower the surface tensions of the mixture so as to improve the miscibility of the ingredients; regulate the sizes of the nucleating air and gas bubbles and hence the cell structure of the foam; and impart a greater stability to the rising foam preventing coalescence of cells, which would otherwise lead to foam collapse.

For flexible slab-stock foams, each formulation requires the presence of a minimum silicone level, below which splits, collapse or coarse-celled foam will result. Good open foam can be obtained at levels above a certain minimum.

Typical of these are the silicone surfactants, eg., the silicone oils and soaps and the siloxane-oxyalkylene block copolymers. Generally up to 4 parts by weight of the surfactants are employed per 100 parts of total diols and polyols, preferably between about 1.0 and about 2.5 parts. Other surfactants may be utilised as emulsifiers in the present invention.

These emulsifiers include ethoxylated alkylphenols, aliphatic alcohols and sulfated aliphatic alcohols, with molecular weights in the range of about 60 to about 3000, preferably in the range of about 300 to about 2000. Generally in the range of about 0.5 to about 50 parts by weight of the emulsifiers are employed per 100 parts of total diols and polyols, preferably between about 10 and about 30 parts.

Of the many different types of catalysts available, tertiary amines and organometallics have been found to be the most useful in the production of flexible foam. Catalysts are used to assist both the gelling (isocyanate/polyol reaction) and blowing (isocyanate/water reaction) reactions in foam production. Different combinations of these catalysts can be used to develop a balance between the two reactions. It is important this balance is right to ensure the gas is entrapped sufficiently in the gelling polymer and the cell walls develop sufficient strength to maintain their structure without collapse or shrinkage. Catalysts also ensure the completeness of the reaction or the 'cure'. Tertiary amines are the most commonly used amines and are mostly used in assisting the blowing reaction although. Different types and concentrations of amines can be selected to satisfy processing requirements such as cream time, rise time, gel times and cure.

Organometallics are used in the gelling reaction. Tin is the most widely used metal within the foam industry. It acts as a Lewis acid and is thought to interact with basic sites in the isocyanate and polyol compounds. Stannous octoate is the most widely used organometallic in the conventional slabstock foam industry. Generally any suitable catalyst may be utilised in the present invention as long as the desired polyurethane foam is produced. The catalyst employed may be any of the catalysts or mixtures of catalysts known to be useful for producing polyurethane foams by the one-step method. Such catalysts include for example, tertiary amines and metallic salts, particularly stannous salts. Typical tertiary amines include, but are not limited to, the following: N-methyl morpholine, Bis(2-dimethylaminoethyl)ether, N- hydroxyethyl morpholine, triethylene diamine, triethylamine and trimethylamine. Typical metallic salts include, for example, the salts of antimony, tin and iron, eg., dibutyltin dilaurate, stannous octoate, and the like. Preferably, a mixture comprised of a tertiary amine and a metallic salt is employed as a catalyst.

The amount of catalyst utilised in the present invention may be any amount that is suitable to yield the desired polyurethane foam. Generally, however, the polyurethane foams of the invention are prepared in the presence of a catalytic amount of a reaction catalyst. The catalyst or catalyst mixture, as the case may be, is usually employed in an amount in the range of about 0.01 and about 2.0, and preferably between about 0.10 and about 1.0 parts by weight per every 100 parts of total di- and polyhydric components.

Other materials which may be incorporated into the hydrophilic foamed compositions of the invention may also include additives such as pigments, colorants, synthetic fibres, mineral fillers, plasticisers, processing aids, anti- oxidants and perfumes. In addition, water retention agents may be utilised in the present invention. Suitable retention agents include alkyl sulfate salts, such as sodium lauryl sulfate. Fillers such as CeC0₃, melamine, gypsum etc may or may not be used.

A thermosetting agent may be utilised to assist compression. The thermosetting agent may be a diol selected from the group consisting of ethyleneglycol, diethyleneglycol, friethyleneglycol, tetraethyleneglycol, 1,4- butanediol, propylene glycol, dipropylene glycol and tripropyleneglycol. Other types of thermosetting agents may be utilised such as polyenes, polydienes or higher conjugates of the aforementioned. A thermosetting agent may not be required if sufficiently high temperature is utilised to permanently buckle the cells and thus achieve permanent compression.

Once the reaction has completed and the resultant foam has finished its expansion the volume of the foam is reduced permanently to 5-70%, more preferably 15-50% of its free rise volume. The term 'free rise volume' is defined as the maximum volume of foam achievable under normal atmospheric pressure and temperature. Compressing the foam is thought to enhance capillary action, which is important for moving water. It is defined as the movement of water within the spaces of a porous material due to the forces of adhesion, cohesion, and surface tension. Capillary action is the result of adhesion and surface tension. Capillary action occurs when the adhesion to the walls is stronger than the cohesive forces between the liquid molecules. Capillary action will take place in a polyurethane foam cell matrix providing that the cell size is sufficiently small enough to allow adhesion of water to the walls of the cell and cause an upward force on the liquid at the edges resulting in a meniscus, which turns upward. The surface tension acts to hold the surface intact, so instead of just the edges moving upward, the whole liquid surface is dragged upward. The height to which capillary action will take water in a polyurethane foam cell matrix is limited by surface tension and will rise higher in a matrix with many small cells than in a matrix with fewer large cells. The methods listed below may be employed in the present invention to reduce volume. A thermosetting agent may not be required if sufficiently high temperature is used in the third step to permanently buckle the cells and thus achieve permanent compression. The reduction in volume of the process is normally accomplished by compressing the expanded foam, which may be compressed in any one direction or a combination of directions.

1. The volume-reducing step can be accomplished by physically compressing the expanded foam and exposing the article to elevated temperature, generally in the range of 100 to 220°C. A thermosetting agent may not be required if sufficiently high temperature is used in the third step to permanently buckle the cells and thus achieve permanent compression. Generally, temperatures in 100-200°C range are considered to be safe when compressing polyurethane foams. However, higher temperatures can be considered under certain circumstances depending on compression time and thickness of the foam. Limiting factor with respect to the compression of the foam is flammability. Free- rise polyurethane foam starts to smoulder, ignite and consequently burn at around 175°C. Heated plates or an oven may be used to increase temperature. Compression time will depend on thickness of the article and temperature of compression. Compressing devices can be removed either immediately after compression or after the foam returns to ambient temperature

2. The article may be compressed by physical means shortly after reaction so that the core temperature remains sufficiently high because of the exothermic reaction that has taken place to achieve permanent compression removal of the compressive device follows the compression step.

3. The volume-reducing step can be accomplished by chemically compressing the free rise expanded foam by reducing/increasing the amount/s of a chemical component/s in the formulation. A person skilled in the art of making polyurethane foam can achieve chemical compression (semi collapse/collapse) in polyurethane foam by reducing the stability. For example; a decrease in silicone, cross-linkers, tin catalyst or increase in blowing index (water, amine, others) to the degree where the cells would coalesce and lead to foam instability. The core temperature of the foam remains sufficiently high because of the exothermic reaction that has taken place to achieve permanent compression.

4. The volume-reducing step can be accomplished by over-packing in a closed mould. The core temperature of the foam remains sufficiently high because of the exothermic reaction that has taken place to achieve permanent compression.

5. The volume-reducing step can be accomplished by expansion of the reacting chemicals taking place at a pressure greater than atmospheric. Generally, the polyurethane foams of the present invention will have, before the permanent volume reduction step, a density in the range of about 5 to 100 kg/m³. Preferably, the density will be in the range of about 15 - 45 kg/m³ and most preferably in the range of about 20-30 kg/m . After compression, the polyurethane foam of the present invention will preferably have the following characteristics as determined by the accompanying test methods. a) Fluid Capacity (FC) greater than 0.9 g/cm³

This test is carried out on a dry sample 90(W) x 90(L) x 25(t) mm, where the thickness (t) of the sample is cut perpendicular to the direction of rise of the foam.

The dry foam sample is accurately measured and the volume is calculated (Dry volume) and then placed into water at room temperature. The foam remains in the water until it is fully saturated (ie: there is no entrapped air). It is useful to squeeze the foam under water to push out any entrapped air and allow it to expand. The foam is then removed from the water taking care to minimise any drips and weighed (Saturated weight). The foam is returned to the water and allowed to absorb more water until a consistent weight is achieved. The saturated weight divided by the dry volume is called the fluid capacity (FC).

FC = Saturated weight (g) /(Dry Volume (mm³)/1000). b) Wet Capacity (WC) greater than 0.95

This property determines the ability to be squeezed out and used again.

This test is carried out on a dry sample cut to 90(W) x 90(L) x 25(t) mm, where the thickness (t) of the sample is cut perpendicular to the direction of rise of the foam.

The sample is fully saturated as per test a) and weighed (Saturated weight 1). As much water as possible is physically removed from the sample as per test d) and weighed (Wet weight 1). The sample is fully saturated as per test a) and reweighed (Saturated weight 2). As much water as possible is physically removed from the sample as per test d) and reweighed (Wet weight 2). WC = (Saturated weight 2) - (Wet weight 2) / (Saturated weight 1) - (Wet weight 1).

c) Equilibrium Moisture (EM) of approximately 40-60%>

The dry foam sample is weighed (Dry weight) and placed into water at room temperature. The sample is fully saturated as per test a). As much water as possible is squeezed out of the foam by hand. The foam is then wrapped in paper towel and squeezed out again. The goal to physically remove as much water as possible. After as much water as possible has been physically removed from the sample it is weighed (Wet weight). The Equilibrium moisture is then calculated as follows.

EM = (Wet weight - Dry weight)/Wet weight x 100 d) Surface Drying (SD) of greater than 50%, preferably greater than 80%, more preferably greater than 95%.

This test is carried out on a dry sample cut to 90(W) x 90(L) x 25(t) mm, where the thickness (t) of the sample is cut perpendicular to the direction of rise of the foam. The sample is fully saturated as per test a). As much water as possible is physically removed from the sample as per test d). Two hundred grams of water is placed into a container of approximate dimensions 250 x 125 x 100mm. The sample is used to absorb as much of the surface water as possible in one minute (The sample may be compressed by hand and wiped over the surface water several times). The amount of water remaining in the container is calculated (Surface weight). The surface- drying factor is calculated as follows.

SD = (200 - Surface Weight(g))/2 % e) Capillary Action (CA) higher than 20mm, preferably greater than 30mm, more preferably greater than 40mm.

This test is carried out on a sample 25(W) x 25(L) x 200(h) mm where the height (h) of the sample is cut perpendicular to the direction of rise of the foam..

The capillary action is measured by immersing the bottom 10(h) mm of a dry sample in water to which water-soluble dye is added. After 3 hours the height of rise is measured from the water level to the upmost position where the dye is not visible. f) Cell count (CC) of at least 8 000 preferably greater than 40 000 more preferably greater than 80 000.

This test is carried out on a dry sample greater than 25(W) x 25(L) x 25(t) mm, where the thickness (t) of the sample is cut perpendicular to the direction of rise of the foam. The amount of cells along a 25mm length is counted using a thread counting glass or other suitable optical instrument. The cell count is made in three dimensions and the amount of cells per cubic centimetre is calculated. The cell count is repeated in three different areas for each dimension and the average is used for calculation. CC = ((cells per 25mm W) x (cells per 25mm L) x (cells per 25mm t))/l 5.625

= cells/cm

For a surface that has been compressed a cell count may be made on uncompressed foam in the same dimension and multiplied by its compression factor.

Eg. For foam compressed to Vi of its original height, compression factor = original height / compressed height = 2 g) Preferably having a Dripping Tendency (DT) less than 35 %.

This test is carried out on a dry sample cut to 90(W) x 90(L) x 25(f) mm, where the thickness (t) of the sample is cut perpendicular to the direction of rise of the foam. The dry foam sample is weighed (Dry weight). The saturated weight of the foam is obtained as per test a). The quantity of water that is picked is determined by (Saturated weight - Dry weight) and the weight of the water that leaks in one minute from the corner of the sample when held by the opposite corner, is determined (Drained weight). The dripping tendency equals 100 times the weight of the water lost divided by the weight of the water picked up.

DT = (100 x (Saturated weight - Drained weight)) / (Saturated weight - Dry weight) h) A Percentage Equilibrium swelling (ES) less than 100%, more preferably less than 75%, more preferably less than 50%.

The dry foam sample is accurately measured and the volume is calculated (Dry volume). The sample is fully saturated as per test a). As much water as possible is physically removed from the sample as per test d). The sample is accurately measured and the volume is calculated (Wet volume). Percentage Equilibrium swelling is calculated as follows.

ES = (Wet volume - Dry volume) / Dry volume x 100 i) A Percentage Dry swelling (DS) less than 100%, more preferably less than 75%», more preferably less than 50%. This test is carried out on a sample dry sample cut to 90(W) x 90(L) x 25(t) mm, where the thickness (t) of the sample is cut perpendicular to the direction of rise of the foam.

The dry foam sample is accurately measured and the volume is calculated (Dry volume). The sample is fully saturated as per test a), accurately measured and the volume is calculated (Saturated volume). Percentage Dry swelling is calculated as follows.

DS = (Saturated volume - Dry volume) / Dry volume x 100 j) A Release factor (RF) greater than 70% This test is carried out on a sample 90(W) x 90(L) x 25(f) mm, where the thickness (t) of the sample is cut perpendicular to the direction of rise of the foam.

The dry foam sample is weighed (Dry weight) and placed into water at room temperature. The sample is fully saturated as per test a), and weighed (Saturated weight). It is then put once through a roller with a

5mm opening and weighed (Release weight). Release factor is calculated as follows.

RF = (Saturated weight - Release weight) / (Saturated weight - Dry weight) x 100 The present invention will be further described in the following

Examples, but the present invention should not be construed as being limited thereto. The Examples, illustrate the preparation of the foam according to an embodiment of the invention and the testing of foam.

Examples Flexible slab foams were prepared from the ingredients (polyisocyanates, polyols, catalysts, foam stabilisers, etc.) set out below. (1) Polyol a) Trade name "Caradol SA36-02" (available from Shell Chemicals): Polyether polyol, polyoxyalkylene triol. High EO content approx 75%. OH No. 36 b) Trade name "Voralux HF505" (available from Dow Chemical

(Australia) limited): polyether polyol, propoxylated glycerine, propoxylated sucrose. Average Molecular Weight >6000, OH No. 29.5, Functionality >3 c) Trade name "HSIOOLV" (available from Bayer Ltd): polymer polyol, Alkenyi Modified Oxyalkylene polymer. OH No. 28 d) Trade name "Voranol CP6001" (available from Dow Chemical (Australia) limited): Triol polyether polyol, capped, 6000 MW, OH No. 27 e) Trade name "Caradol SP33-03" (available from Shell Chemicals): Suspension of styrene-acrylonitrile particles in a propylene oxide /ethylene oxide based polyether poylol. OH No.

33

(2) Diol a) Trade name "TPG" (available from Dow Chemical (Australia) limited): Tripropylene glycol. OH No.600

(3) Polyisocyanate

a) Trade name "VORANATE T-80 TYPE 1 TDI" (available from Dow Chemical (Australia) limited): Toluene diisocyanate. 80% 2,4-toluene diisocyanate, 20% 2,6-toluene diisocyanate

(4) Catalyst a) Trade name "DABCO 33-LV CATALYST" (available from Air products Pty. Ltd): Tertiary Amines, Mixture of Dipropylene glycol and Triethylenediamine. OH No. 561

b) Trade name "KOSMOS 29" (available from TH. Goldschmidt AG): Tin catalyst, Tin-(II)-isooctoate

(5) Surfactant (Stabiliser) a) Trade name "TEGOSTAB B 8050" (available from TH.

Goldschmidt AG): Silicone surfactant, Polyethersiloxane. b) Trade name "TEGOSTAB BF 2370" (available from TH. Goldschmidt AG): Silicone surfactant, Polyethersiloxane.

(6) Filler a) Trade name "Omyacarb 10" (available from Omya Australia Pty limited): Calcium Carbonate. b) Trade name "Gypsum G75" (available from Commercial Minerals): Calcium sulphate.

(7) Crosslinker a) Trade name "Diethanolamine LFG 85%" (available from

International Sales and Marketing Pty limited): Alkanolamine. OH No.1362

Flexible slab foams were prepared using the following methods. In these methods batches of flexible polyurethane foams based on polyether polyols and on diisocyanates of the TDI 80/20 type were prepared. The formulations were based on 100 parts by weight total polyol (including diol), the necessary additives and total water. The amount of TDI used in the formulations was calculated using the OH numbers (given by the supplier) and TDI requirement factor equal to 0.00155 x OH No. The following formula was used when calculating the amount of TDI required in p.b.w. per 100 parts polyol. p.b.w. TDI = (Index/100) x 0.00155 x (sum of polyol OH No's x p.b.w. + 6239 x total water p.b.w. + sum of additives OH No's x p.b.w.). All chemicals were weighed to an accuracy of ± 1%. The mixing speed was 2575 ± 100 rpm.

Method A

An open top metal box, (38cm x 38cm x 53cm high) was lined with paper to prevent sticking of the material to the walls. The polyol was weighed into a 2.21t-mixing container. Water, silicone, amines were weighed in this sequence into a mixing container and stirred with a spatula until it appeared homogeneous (about 10 seconds). The temperature was checked and adjusted to 21±1°C. TDI 80/20 was weighed in a 1 -litre jug. Tin catalyst was added to the polyol blend and stirred with an electric stirrer for 10 seconds. Whilst stirring, pre-weighed TDI 80/20 was added. A timing device was started immediately after the TDI 80/20 was added to the polyol/water/catalyst mixture. The resultant mixture was mixed for 10 seconds and deposited into the paper lined metal box. The time for the mixture to start to produce gas, losing clarity and become creamy was recorded as the cream time. The time at which the expansion finished was recorded as the rise time. After 10 minutes the foam was removed from the box and placed in an oven at 90°C for 20 minutes to cure the surface. The foam was cut at a perpendicular to the direction of rise through the centre and a sample for testing was prepared. After curing 24 hours at room temperature the foam was then compressed to 25% (Compression factor of 4) of its original height and placed into an preheated oven at 170°C, for 2 hrs. The foam was removed from the oven whilst still compressed and allowed to cool slowly until it reached ambient temperature. The compression plates were then removed.

Method B

An open top metal box, (38cm x 38cm x 53cm high) was lined with paper to prevent sticking of the material to the walls. The polyol was weighed into a 2.21t-mixing container. Water, silicone, amines were weighed in this sequence into a mixing container and stirred with a spatula until it appeared homogeneous (about 10 seconds). The temperature was checked and adjusted to 21±1°C. TDI 80/20 was weighed in a 1-litre jug. Tin catalyst was added to the polyol blend and stirred with an electric stirrer for 10 seconds. Whilst stirring, pre-weighed TDI 80/20 was added. A timing device was started immediately after the TDI 80/20 was added to the polyol/water/catalyst mixture. The resultant mixture was mixed for 10 seconds and deposited into the paper lined metal box. The time for the mixture to start to produce gas, losing clarity and become creamy was recorded as the cream time. The time at which the expansion finished was recorded as the rise time. After 10 minutes the foam was removed from the box and placed in an oven at 90°C for 20 minutes to cure the surface. The foam was cut at a perpendicular to the direction of rise through the centre and a sample for testing was prepared. After curing 24 hours at room temperature the foam was then compressed with heated plates (@ 185°C) that were removed at the end of the heating cycle (13.5 minutes).

Method C

A metal mould, (34cm x 34cm x 10cm) was coated with wax to prevent material adhesion to the walls. The polyol was weighed into a 2.21t-mixing container then water, silicone, amines were weighed in this sequence into a mixing container and stirred with a spatula until it appeared homogeneous (about 10 seconds). The temperature was checked and adjusted to 21±1°C. TDI 80/20 was weighed in a 1 -litre jug. Tin catalyst was added to the polyol blend and stirred with an electric stirrer for 10 seconds. Whilst stirring, pre-weighed TDI 80/20 was added. A timing device was started immediately after the TDI 80/20 was added to the polyol/water/catalyst mixture. The resultant mixture was mixed for 10 seconds and deposited into the metal mould and the lid was clamped tight. After 30 minutes the mould was placed in an oven at 90°C for 20 minutes to cure. The foam was cut at a perpendicular to the direction of rise through the centre and a sample for testing was prepared. The foam was removed from the oven whilst still compressed and allowed to cool slowly until it reached ambient temperature before the mould was opened.

Method D

An open top metal box, (38cm x 38cm x 53cm high) was lined with paper to prevent sticking of the material to the walls. The polyol was weighed into a 2.21t-mixing container. Weigh the water, silicone, amines in this sequence into the mixing container and stir with a spatula until it appeared homogeneous (about 10 seconds). The temperature was checked and adjusted to 21±1°C. TDI 80/20 was weighed in a 1-litre jug. Tin catalyst was added to the polyol blend and stirred with an electric stirrer for 10 seconds. Whilst stirring, pre-weighed TDI 80/20 was added. A timing device was started immediately after the TDI 80/20 was added to the polyol/water/catalyst mixture. The resultant mixture was mixed for 10 seconds and deposited into the paper lined metal box. The time for the mixture to start to produce gas, losing clarity and become creamy was recorded as the cream time. The time at which the expansion finished was recorded as the rise time. After 10 minutes the foam was removed from the box and placed in an oven at 90°C for 20 minutes to cure the surface. The foam was cut at a perpendicular to the direction of rise through the centre and a sample for testing was prepared. Compression is achieved by collapsing the foam with reduced silicone surfactant. In this example the compression factor equals the full rise height of the foam before collapse divided by the collapsed height of the foam.

A summary of the formulations and test results is set out in Table 1 TABLE 1

^: Example F is for comparative purposes and is not claimed as part of the current invention.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It will be understood that the present invention encompasses all such variations and modifications that fall within the spirit and scope.

Claims

1. A process of preparing an open cell hydrophilic foam comprising the steps of: reacting in a single step, a reaction mixture to produce an open cell hydrophilic polyurethane foam, the reaction mixture comprising an organic polyisocyanate, water, a reaction catalyst and a polyol component including a poly(oxyalkylene) polyol having an ethylene oxide content of at least 50%; and reducing the volume of the foam to 5-70% of the original volume.

2. The process of claim 1, wherein the reaction mixture includes a thermosetting agent.

3. The process of claim 1, wherein the ethylene oxide content is 60-90%.

4. The process of claim 1, wherein the step of reducing the volume of the foam is accomplished by compressing the expanded foam at an elevated temperature in the range of 100-220°C.

5. The process of claim 1, wherein the polyol component has a molecular weight in the range of 3,000 to 10,000.

6. The process of claim 4, wherein compression step occurs shortly after the single step reaction.

7. The process of claim 1, wherein the volume-reducing step is accomplished by expanding the reacting chemicals at a pressure greater than atmospheric.

8. The process of claim 1, wherein the volume-reducing step involves chemically compressing the free-rise expanded foam by varying the amount of chemical components in the reaction mixture.

9. The process of claim 1, wherein the organic polyisocyanate is selected from the group consisting of toluene diisocyanate, ethylene diisocyanate, propylene diisocyanate, methyl ene-bis-4-phenyl isocyanate, 3,3'bis-toluene-4,4'-diisocyanate, hexamethylene diisocyanate, napthalene-l,5-diisocyanate polymethylene polyphenylene diisocyanate, mixtures thereof.

10. The process of claim 1, wherein the amount of isocyanate provides an isocyanate index of at least about 50 and les than 115.

11. The process of claim 1, wherein the amount of isocyanate provides an isocyanate index in the range of about 50-100.

12. The process of claim 1, wherein the water is provided in the range of about 1 to about 20 parts water, per 100 parts by weight of the di-and polyhydric components.

13. The process of claim 1 wherein the water is provided in the range of about 2 to about 10 parts water, per 100 parts by weight of the di-and polyhydric components.

14. The process of claim 1 wherein the water is provided in the range of about 3 to about 5 parts water, per 100 parts by weight of the di-and polyhydric components.

15. The process of claim 1, wherein the catalysts are selected from the group consisting of tertiary amines and metallic salts and mixtures thereof.

16. The process of claim 1, wherein the polyol is selected from the group consisting of: polyoxypropylene diols; polyoxypropylene triols; polyoxypropylene tetrols; polyoxypropylene pentols; polyoxypropylene hexols ethylene-oxide-capped diols, triols, tetrols, pentols or hexols; random and block polymers of the above in which the polyol is made with both ethylene and propylene oxides; graft or copolymer polyols, which contain stable dispersions of a solid particulate polymeric phase in the liquid polyol phase; and cross linkers.

17. The process of claim 2, wherein the thermosetting agent is a diol selected from the group consisting of ethyleneglycol, diethyleneglycol, triethyleneglycol, tetraethyleneglycol, 1,4-butanediol, propylene glycol, dipropylene glycol tripropyleneglycol, polyenes, polydienes or higher conjugates thereof.

18. The process of claim 1, wherein the foam has a density in the range of 5 to 100 kg/m³ prior to the volume reduction step.

19. An open cell hydrophilic polyurethane foam formed by the process of claim 1.

20. An open cell hydrophilic polyurethane foam having at least one of the following characteristics: a) Fluid Capacity (FC) greater than 0.9 g/cm³; b) Wet Capacity (WC) > 0.95; c) Equilibrium Moisture (EM) of approximately 40-60%; d) Surface Drying (SD) of greater than 50%, ; e) Capillary Action (CA) higher than 20mm; and f) Cell count (CC) of at least 8,000.

21. The foam of claim 20 wherein characteristics including a surface drying greater than 80%.

22. the foam of claim 20 wherein the characteristics include surface drying greater than 95%.

23. The foam of claim 20 wherein the list of characteristics include a dripping tendency (DT) less than 35%.

24. The foam of claim 20 wherein the equilibrium swelling (ES) is less than 100%.

25. The foam of claim 20 wherein the percentage dry swelling (DS) is less than 100%.

26. An open cell hydrophilic polyurethane foam formed by the process of claim 1 having at least one of the following characteristics

a) Fluid Capacity (FC) greater than 0.9 g/cm³; b) Wet Capacity (WC) > 0.95; c) Equilibrium Moisture (EM) of approximately 40-60%;

d) Surface Drying (SD) of greater than 50%, ; e) Capillary Action (CA) higher than 20mm; and f) Cell count (CC) of at least 8,000.

27. Articles made from the foam of claims 20 or 26.