Polyurethane froth foams

Abstract: A process for the manufacture of a polyurethane froth foam is provided. The process, which comprises contacting a polyurethane forming formulation with an inert gas under conditions which produce a froth, uses a formulation which contains a chain extender which is an alkoxylated bisphenol A. Optionally a second chain extender which is a linear glycol can also be used. The polyurethane froth foams produced are thermoformable whilst exhibiting good shape retention at ambient temperature.

Description: The present invention relates to novel polyurethane froth foams for use as a backing for coverings such as carpets or upholstery. In particular, the invention relates to novel polyurethane froth foams which can be formed or moulded into shape when hot and which retain their shape when cold. The production of polyurethane froth foams, for use as a backing for coverings such as carpets, artificial grass, sports surfaces and the like, is a known process. Such polyurethane froth foams can be prepared, for example, by mixing a two-component reactive polyurethane-forming mixture with an inert gas (i.e. nitrogen, air etc), under froth-generating conditions of high shear, usually in the presence of catalysts and froth stabilisers. The polyurethane-forming mixture is chosen so that it reacts slowly thereby allowing ample time for a froth to be formed in the mixer. Once the polyurethane froth has been formed it is usually contacted, in an uncured state, with an appropriate covering substrate, e.g. vinyl sheet, textile tufts, etc. to produce the finished foam backed covering. The finished foam backed covering is then cured at elevated temperature. A typical example of this process has been described in detail in Cellular Polymers Vol. 4, pages 179-183 (1985). Similarly, GB-A-1460863 discloses polyurethane froth foam compositions comprising a polyether polyol, a polyisocyanate and as a chain extender an aromatic diamine or a glycol such as diethylene glycol. The foam compositions may be applied to a substrate such as a carpet prior to airing. Foamed backed coverings produced by the processes described above are flexible but exhibit no shape retention. For some applications however, for example in the automotive industry, there is a demand for coverings which show shape retention at ambient temperatures but which are thermoformable, i.e. mouldable or formable at elevated temperatures. Such materials have the advantage that they can be bought or manufactured in sheet form and subsequently thermoformed into the complex shapes required to cover the interiors of automobiles. One approach to rendering such coverings thermoformable is to incorporate into the covering a thermoplastic rigid polymer such as a polypropylene, a polyester, a polyamide or a polycarbonate. This can be done for example by bonding a sheet or a non-woven fleece of the thermoplastic rigid polymer to the covering or by incorporating a thermoplastic rigid polymer in powder form into the polyurethane froth foam. A new method of rendering polyurethane froth foamed backed coverings thermoformable has now been discovered which avoids the need to use a thermoplastic material. The new method involves modifying the structure of the polyurethane by incorporating into the polyurethane froth foam forming mixture one or more chain extenders which render the cured polyurethane froth foam thermoformable whilst at the same time keeping it sufficiently stiff at ambient temperatures to give good shape retention. Accordingly, the present invention provides a process for the manufacture of a thermoformable polyurethane froth foam which process comprises contacting a polyurethane forming formulation with an inert gas under conditions which produce a froth of the polyurethane forming formulation characterised in that the polyurethane forming formulation comprises a polyfunctional isocyanate, a polyfunctional alcohol, and a chain extender which is an alkoxylated bisphenol A. The function of the chain extender is to render the final cured polyurethane froth foam thermoformable. In EP-A-0 269 346, from which this is a divisional application, we describe processes similar to those described herein in which the chain extender is an aromatic amine having the formula I wherein the R groups are independently selected from hydrogen groups and the R¹ and R² groups are independently selected from hydrogen, hydroxy functionalised alkyl groups or hydroxy functionalised poly(oxyalkylene) groups; with the proviso that R¹ and R² are not both hydrogen. The alkoxylated bisphenol A is preferably one alkoxylated with between 1 and 6 moles of either ethylene oxide, propylene oxide or mixtures thereof per mole of bisphenol A. Polyurethane froth foam formulations containing the chain extender of the present invention produce cured froth foams with a satisfactory degree of shape retention at or near room temperature and which are thermoformable at temperatures below 200°C. Such cured froth foams when heated can be easily thermoformed by the action of mechanical or vacuum pressing. Whilst the cured froth foams described above have the advantage that they are easily thermoformed and have adequate shape retention characteristics, it has also been found that the shape retention characteristics can be further improved by having a second chain extender present in the froth foam formulation. Accordingly, in a preferrred aspect of the present invention there is provided a process for the manufacture of a polyurethane froth foam which process comprises contacting a polyurethane forming formulation with an inert gas under conditions which produce a froth of the polyurethane formulation characterised in that the polyurethane forming formulation comprises a polyfunctional isocyanate, a polyfunctional alcohol, a chain extender as described above and a second chain extender comprising a linear glycol. The effect of the second chain extender is to improve the rigidity and hence shape retention of the cured froth foam. Suitable examples of linear glycols include, monoethylene glycol, monopropylene glycol, diethylene glycol, and dipropylene glycol. Most preferred is monoethylene glycol. Since the two chain extenders influence the properties of the cured froth foam in different ways it will be appreciated that the properties of the final foam will be influenced by (a) the relative proportions of the two, and (b) the absolute proportions of each in the polyurethane foam forming formulation. Considering first the relative proportions of the two chain extenders, it can be said that in general the higher the proportion of the linear glycol relative to the alkoxylated bisphenol A the better the shape retention and the worse the thermoformability of the cured foam. Hence for most applications there is a compromise between having good shape retention and having a cured foam which is thermoformable at a temperature below which thermal degradation of the foam occurs. As regards the absolute levels of the two chain extenders, the more second chain extender there is present, the more shape retentive the final product will be whilst the more first chain extender there is present the easier it will be to thermoform the product. Preferably, each chain extender is present in amounts corresponding to less than 20% by weight of the polyfunctional alcohol used. As mentioned earlier, it is desirable that the cured polyurethane foam should be thermoformable at a temperature below which thermal degradation occurs. In practice this means that the polyurethane foam should be thermoformable at a temperature of less than 200°C, preferably in the range 130-180°C. The polyfunctional isocyanates which can be used in the present process will be known to those skilled in the art. Suitable examples include individual or mixtures of the isomers of aromatic diisocyanates such as toluene diisocyanate (TDI), and xylene diisocyanates, difunctional aliphatic or cycloaliphatic isocyanates having between 2 and 18 carbon atoms, preferably 4-12 carbon atoms and isomers and oligomers of di(4-isocyanatophenyl) methane (MDI). Preferably the polyfunctional isocyanate is MDI, an MDI prepolymer, an MDI variant, or a mixture thereof. In addition to the above, prepolymers of polyfunctional isocyanates and polyfunctional alcohols or amines can be used. Although the polyfunctional polyol used can be any alcohol having two or more reactive hydroxyl groups it is suitably a polyether polyol. The term polyether polyol, which is well known in the art, includes alkylene oxide adducts of (1) low molecular weight diols and triols or naturally occurring polyols (2) non reducing sugars and derivatives thereof and (3) phosphoric, phosphorous, and polyphosphoric acids. Examples of such adducts are the alkylene oxide adducts of ethylene glycol, propylene glycol, glycerol, trimethylol propane, the isomeric butanediols, and hexanediols, octanediols. Alkylene oxide adducts of pentaerythritol, sorbitol, arabitol, mannitol, alkyl glucoside, alkylene glycol glucosides and glycerol glucosides are also contemplated, as are adducts of alkylene diamines and hydrazines. In general it is desirable that the alkylene oxide used to form the adduct is a lower alkylene oxide having from 2 to 4 carbon atoms. Preferred examples are ethylene oxide, propylene oxide, the butylene oxides or mixtures thereof. Polyether polyols containing additional polymeric matter, e.g. polymer polyols, may also be employed. Mixtures of polyether polyols or mixtures of polyether polyols and polymer polyols can be used. When both chain extenders are used for balanced thermoformability and shape retention, a mixture of polyfunctional alcohols and polymer polyols is tailored to obtain the desired mechanical properties of the final froth foam. When emphasis is placed upon easy thermoformability, e.g. for vacuum forming applications, the first chain extender is used as above together with small amounts of ethylene glycol and the polyfunctional alcohols are preferably diols together with higher functionality polyfunctional alcohols and/or polymer polyols used in smaller amounts as required to obtain the correct mechanical properties. In addition to the components described above, the polyurethane froth foam formulation may also contain other additives (e.g. surfactants, catalysts, fillers, etc.) which are routinely used in making froth foams. The polyurethane forming formulations of the present invention can be frothed using standard techniques, coated on to an appropriate covering substrate and thereafter cured. It has been found that polyurethane froth foam backed coverings containing the additives described above, and in particular those produced according to the present invention, show particularly good shape retention/thermoformability properties without the weight and processing disadvantages of prior art materials. This is particularly so when the thickness of the polyurethane froth foam is less than 0.5 cm. The invention is now illustrated by the following Example. Example 1 A polyurethane froth formulation was prepared according to the composition given in Table 1. Dionol 220 (ex Akzo Chemie) was used as the alkoxylated bisphenol A. The formulation was frothed with air in a Mondomix Mixer 'T-Model' and knife coated on to release paper. The froth coating was then cured in an oven at 150° for 5 minutes to form a frothed elastomer sheet of 0.35 cm thickness. The thermoformability and shape retention at ambient and 80°C was measured. The results of the thermoformability and shape retention tests are also given in Table 1. Dionol 220 = 1 mole of bisphenol A ethoxylated with 4 mole of ethylene oxide. Polyurax polyol PPG 2025 - 2000 MW polypropylene glycol (ex BP Chemicals). Polyurax polyol U2022 - Polymer polyol ca 20% by weight 50/50 styrene acrylonitrile copolymer in 5000 MW polyether polyol CP-3 (ex BP Chemicals). Polyurax RA 4006 - Quaternised fatty amine salt (ex BP Chemicals). The shape retention and thermoformability tests have been described recently in the SPI-FSK proceedings (Aachen) "Polyurethane World Congress" - Oct 1987 - paper by P. Berthevas, A. Fanget and G. Catouillat. However tests to demonstrate such problems can easily be developed by those skilled in the art.

Claims: A process for the manufacture of a thermoformable polyurethane froth foam which process comprises contacting a polyurethane forming formulation with an inert gas under conditions which produce a froth of the polyurethane forming formulation characterised in that the polyurethane forming formulation comprises a polyfunctional isocyanate, a polyfunctional alcohol and a chain extender which is an alkoxylated bisphenol A. A process as claimed in Claim 1, characterised in that the alkoxylated bisphenol A is one alkoxylated with between 1 and 6 moles of ethylene oxide, propylene oxide, or mixtures thereof per mole of bisphenol A. A process as claimed in Claim 1 or Claim 2, characterised in that the polyurethane forming formulation further comprises, as a second chain extender, a linear glycol. A process as claimed in Claim 3, characterised in that the linear glycol is selected from the group consisting of monoethylene glycol, monopropylene glycol, diethylene glycol and dipropylene glycol. A process as claimed in any preceding claim, characterised in that the alkoxylated bisphenol A chain extender comprises up to 20% by weight of the total polyfunctional alcohol used. A process as claimed in Claim 3, characterised in that the second chain extender comprises up to 20% by weight of the total polyfunctional alcohol used. A process as claimed in any preceding claim, characterised in that the polyfunctional alcohol is a diol. A mixture consisting essentially of (a) up to 20% by weight of a chain extender as defined in Claim 1, (b) up to 20% of a second chain extender as defined in Claim 3 and (c) one or more polyfunctional alcohols. A polyurethane froth foam backed covering comprising a covering substrate bonded to a layer of cured polyurethane froth foam produced by a process as claimed in any one of Claims 1 to 7. A polyurethane froth foam backed covering comprising a covering substrate bonded to a layer of cured polyurethane froth foam containing in reacted form up to 20% by weight of a chain extender as defined in Claim 1. A polyurethane froth foam backed covering comprising a covering substrate bonded to a layer of cured polyurethane froth foam containing in reacted form up to 20% by weight of the chain extender as defined in Claim 3. A polyurethane froth foam backed covering as claimed in any of Claims 9 to 11, characterised in that the layer of cured polyurethane froth foam is less than 0.5 cm thick. A process for preparing a polyurethane froth foam backed covering which comprises coating a covering substrate with a layer of froth of a polyurethane forming formulation as defined in any one of Claims 1 to 7 and thereafter curing the froth.

Inventors: BERTHEVAS PAUL RENE BP CHEMICA, FANGET ALAIN FRANCOIS BP CHEMI, BERTHEVAS, PAUL RENE BP CHEMICALS (SUISSE) SA, FANGET,ALAIN FRANCOIS BP CHEMICALS (SUISSE) SA
Applicants: POLYOL INT BV, POLYOL INTERNATIONAL B.V.
Application year: 1988
Main classification: C08G18
IPC codes: D06N3, C08G18, C08J9