WO2001032791A1

WO2001032791A1 - Urethane-group containing insulating coating

Info

Publication number: WO2001032791A1
Application number: PCT/EP2000/009491
Authority: WO
Inventors: Andy Louis Celine Mertens; Eric Bertrand
Original assignee: Huntsman International Llc
Priority date: 1999-11-04
Filing date: 2000-09-28
Publication date: 2001-05-10
Also published as: AU7908800A

Abstract

Process for preparing a urethane group-containing insulating coating comprising the step of reacting a polyisocyanate compound with a compound containing at least two isocyanate-reactive hydrogen atoms in the presence of a filler material which comprises polyisocyanate-based aerogel or xerogel granules having a diameter of larger than 200 νm.

Description

DESCRIPTION

URETHANE-GROUP CONTAINING INSULATING COATING

The present invention relates to a urethane group-containing insulating coating for hollow bodies such as pipes used in subterranean or submerged pipelines for recovery of oil, gas, slurries or the like materials from a subterranean well.

Underwater pipelines are most frequently used for transporting hydrocarbons from the offshore reservoirs to shore and onshore transport between reservoirs and locations. With such substances, it is important that the temperature within the pipeline does not fall below a certain level, otherwise hydrate and wax formation and deposition occur. The temperature of the hydrocarbons increases with the depth of the reservoirs. In the transportation of such materials it is necessary to prevent heat loss from the hydrocarbons and this is generally addressed by providing an insulating coating around the pipeline. Underwater pipelines may also require a weight coating for several purposes including the need to weigh the pipeline down and so maintain the position of the pipe on the seabed and to form a protective cover around the pipeline.

Polyurethane foams and elastomers have been used to insulate oil and gas pipes in offshore and onshore applications. The requirements for these insulation materials are more stringent now that deep-sea wells are being exploited. For example, the heat resistance of these materials needs to be increased from 120°C to 160°C and the pressure resistance from 50 bar (at 500 m depth of immersion) to 250 bar (at 2500 m depth of immersion). In order to fulfil these requirements it has been proposed to incorporate temperature- and pressure-resistant hollow microspheres into these polyurethane coatings.

WO 96/28684 describes a pipe having an anti-corrosion coating and a protective weight coating of a urethane based copolymer applied over said anti-corrosion coating, said protective weight coating incorporating a high density filler material such as an inorganic particulate material (e.g. micro fine barium sulfate) which is dosed into the urethane during the molding process.

WO 99/03922 describes an insulating polyurethane coating for pipes used in offshore applications, particularly for pipes used at depths of more than 500 m; said coating containing organic or mineral hollow microspheres with an average particle size of between 5 and 200 μm and a density of between 0.1 and 0.8 g/cm³.

EP 896976 describes syntactic polyurethane foams having a high compressive strength comprising the use of hollow microspheres filled with a hydrocarbon, air or vacuum. The microspheres have average diameters ranging from 80 to 200 microns and are added in an amount of 20 to 80 wt% on the foam.

The present invention aims to overcome the problems associated with known pipe coatings and to provide an improved pipe coating which displays both good insulating properties and gives weight to the pipeline. According to the present invention a process for preparing a urethane-, urea- and/or isocyanurate group-containing insulating coatings for hollow bodies is provided by reacting a polyisocyanate compound with a compound containing at least two isocyanate- reactive hydrogen atoms in the presence of catalysts and optionally other auxiliaries whereby at least one of the reaction compositions contains polyisocyanate based aerogel or xerogel granules having a diameter of larger than 200 μm.

By using these polyisocyanate based aerogel or xerogel granules in the urethane-based coating syntactic foams are obtained having better insulation properties and lower densities than the foams of the prior art. Also these aerogel or xerogel granules can be used at a lower loading than the microspheres of EP 896976 and WO 99/03922 to obtain an insulating coating of low thermal conductivity and low density.

Because these aerogel or xerogel granules are also based on polyisocyanate a better compatibility with the other foam-forming ingredients is obtained; the risk of tension cracks at the interface is reduced. The isocyanate-based aerogel or xerogel granules for use in the presently claimed coating are prepared by mixing a polyisocyanate and a catalyst and optionally a polyninctional isocyanate-reactive compound in a suitable solvent, maintaining said mixture in a quiescent state for a sufficiently long period of time to form a polymeric gel, and drying the thus formed gel. This preparation method is described in WO 95/03358, WO 96/36654, WO 96/37539, WO 98/44013 and WO 98/44028, all incorporated herein by reference.

Polyisocyanates for use in the preparation of the aerogel or xerogel granules include aliphatic, cycloaliphatic, araliphatic and aromatic polyisocyanates known in the literature for use generally in the production of polyurethane/polyisocyanurate materials. Of particular importance are aromatic polyisocyanates such as tolylene and diphenylmethane diisocyanate in the well known pure, modified and crude forms, in particular diphenylmethane diisocyanate (MDI) in the form of its 2,4'-, 2,2'- and 4,4'-isomers (pure MDI) and mixtures thereof known in the art as "crude" or polymeric MDI (polymethylene polyphenylene polyisocyanates) having an isocyanate functionality of greater than 2 and the so-called MDI variants (MDI modified by the introduction of urethane, allophanate, urea, biuret, carbodiimide, uretonimine or isocyanurate residues). The polyisocyanate is used in the aerogel/xerogel preparation process in amounts ranging from 0.5 to 30 % by weight, preferably from 1.5 to 20 % by weight and more preferably from 3 to 15 % by weight based on the total reaction mixture.

Trimerisation catalysts for use in the aerogel/xerogel preparation method include any isocyanate trimerisation catalyst known in the art such as quaternary ammonium hydroxides, alkali metal and alkaline earth metal hydroxides, alkoxides and carboxylates, for example potassium acetate and potassium 2-ethylhexoate, certain tertiary amines and non-basic metal carboxylates, for example lead octoate, and symmetrical triazine derivatives. Specific preferred trimerisation catalysts for use in the present method are Polycat 41 available from Abbott Laboratories, and DABCO TMR, TMR-2, TMR-4 and T 45 available from Air Products, and potassium salts such as potassium octoate, potassium hexanoate, potassium 2-ethyl hexanoate and potassium acetate.

Another class of catalysts that can be used in addition to the trimerisation catalysts are the conventionally known catalysts in the polyurethane industry that catalyze the formation of amines, urethane, uretidione and carbodiimide groups. Specific examples include aliphatic and aromatic tertiary amines, for example, N,N-dimethylcyclohexylamine; alkanolamines; organo-metallic compounds, especially tin compounds, for example, dibutyltin dilaurate; trialkylphosphines and dialkylarylphosphines; phospholine oxides. Combinations of the above catalysts may be used as well.

The polyisocyanate/catalyst weight ratio varies between 5 and 1000, preferably between 5 and 500, most preferably between 10 and 200. The preferred polyisocyanate/catalyst weight ratio depends on the amount of polyisocyanate used, the reaction cure temperature, the solvent used, additives used. The solvent to be used in the aerogel/xerogel preparation method should be a solvent for the monomeric (non-reacted) polyisocyanate as well as for the polymeric (reacted) polyisocyanate. The solvent power should be such as to form a homogeneous solution of non-reacted compounds and to dissolve the reaction product or at least prevent flocculation of the reaction product. Solvents with a solubility parameter between 0 and 18 MPa¹/ and a hydrogen bonding parameter H between 0 and 15 MPa¹/ are most suitable.

Suitable solvents include hydrocarbons, dialkyl ethers, cyclic ethers, ketones, alkyl alkanoates, aliphatic and cycloaliphatic hydrofluorocarbons, hydrochlorofluorocarbons, chlorofluorocarbons, hydrochlorocarbons, halogenated aromatics and fluorine-containing ethers. Mixtures of such compounds can also be used. Suitable hydrocarbon solvents include lower aliphatic or cyclic hydrocarbons such as ethane, propane, n-butane, isobutane, n-pentane, isopentane, cyclopentane, neopentane, hexane and cyclohexane.

Suitable dialkyl ethers to be used as solvent include compounds having from 2 to 6 carbon atoms. As examples of suitable ethers there may be mentioned dimethyl ether, methyl ethyl ether, diethyl ether, methyl propyl ether, methyl isopropyl ether, ethyl propyl ether, ethyl isopropyl ether, dipropyl ether, propyl isopropyl ether, diisopropyl ether, methyl butyl ether, methyl isobutyl ether, methyl t-butyl ether, ethyl butyl ether, ethyl isobutyl ether and ethyl t-butyl ether. Suitable cyclic ethers include tetrahydrofuran. Suitable dialkyl ketones to be used as solvent include acetone, cyclohexanone, methyl t- butyl ketone and methyl ethyl ketone.

Suitable alkyl alkanoates, which may be used as solvent, include methyl formate, methyl acetate, ethyl formate, butylacetate and ethyl acetate. Suitable hydrofluorocarbons which may be used as solvent include lower hydro fluoroalkanes, for example difluoromethane, 1,2-difluoroethane, 1,1,1,4,4,4- hexafluorobutane, pentafluoroethane, 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane, pentafluorobutane and its isomers, tetrafluoropropane and its isomers and pentafluoropropane and its isomers. Substantially fluorinated or perfluorinated (cyclo)alkanes having 2 to 10 carbon atoms can also be used.

Suitable hydrochlorofluorocarbons, which may be used as solvent, include chlorodifluoromethane, l,l-dichloro-2.2.2-trifluoroethane, 1 , 1 -dichloro- 1 -fluoroethane, 1- chloro-l,l-difluoroethane, 1 -chloro-2-fluoroethane and l,l ,l,2-tetrafluoro-2-chloroethane. Suitable chlorofluorocarbons, which may be used as solvent, include trichlorofluoromethane, dichlorodifluoromethane, trichlorotrifluoroethane and tetrafluorodichloroethane. Suitable hydrochlorocarbons, which may be used as solvent, include 1- and 2- chloropropane and dichloromethane.

Suitable halogenated aromatics include monochlorobenzene and dichlorobenzene. Suitable fluorine-containing ethers which may be used as solvent include bis- (trifluoromethyl) ether, trifluoromethyl difluoromethyl ether, methyl fluoromethyl ether, methyl trifluoromethyl ether, bis-(difluoromethyl) ether, fluoromethyl difluoromethyl ether, methyl difluoromethyl ether, bis-(fluoromethyl) ether, 2,2,2-trifluoroethyl difluoromethyl ether, pentafluoroethyl trifluoromethyl ether, pentafluoroethyl difluoromethyl ether, 1,1,2,2-tetrafluoroethyl difluoromethyl ether, 1,2,2,2- tetrafluoroethyl fluoromethyl ether, 1 ,2,2-trifluoroethyl difluoromethyl ether, 1 , 1 -difluoroethyl methyl ether, l,l,l,3,3,3-hexafluoroprop-2-yl fluoromethyl ether.

Preferred solvents are dichloromethane, methyl ethyl ketone, acetone, tetrahydrofuran, monochlorobenzene, trichlorofluoromethane (CFC 11), chlorodifluoromethane (HCFC 22), l,l,l-trifluoro-2-fluoroethane (HFC 134a), 1,1-dichloro-l-fluoroethane (HCFC 141b) and mixtures thereof such as HCFC 141b/CFC 1 1 mixtures, 1,1,1,3,3-pentafluoropropane (HFC 245fa), 1,2-difluoroethane (HFC 152), difluoromethane (HFC 32) and 1,1,1,3,3- pentafluorobutane (HFC 365mfc).

Another suitable solvent is liquid carbon dioxide (CO2). Liquid carbon dioxide may be used under various pressures (above 63 bar) and temperatures. Also sub- or supercritical carbon dioxide can be used as a solvent. The solvent power of sub- or supercritical carbon dioxide can be adjusted by adding suitable modifiers such as lower alkanes (C1-C4), methanol, ethanol. acetone, HCFC 22, dichloromethane in levels of 0.1 to 50 % by volume. In case liquid carbon dioxide is used as solvent it has been shown to be an advantage to use as polyisocyanate in the preparation of the aerogels/xerogels a fluorinated isocyanate - ended prepolymer made from a polyisocyanate and a fluorinated isocyanate-reactive compound such as a fluorinated monol or diol.

Alternatively sub- or supercritical hydrofluorocarbons may be used as sole solvent or admixed with CO2- The isocyanate-reactive group present in the (co)polymer used in the aerogel/xerogel preparation method is an OH, COOH, NH2 or NHR group, preferably an OH group.

Examples of suitable classes of (co)polymers are polyacrylates, polystyrenes, polyketones, bisphenol A resins, hydrocarbon resins, polyesters, polyaldehyde-keton resins, resols, novolaks, neutral phenolic resins, polymethacrylates, polyacrylonitrile, polyvinylacetate, PET derivatives, polyamides, cellulose, polyethers, modified polyethylene and polypropylene, polybutadienes and alkyd resins.

A particularly preferred class of (co)polymers are those derived from ethylenically unsaturated monomers; preferred are styrene, acrylic acid and acrylic acid ester derivatives such as methylacrylate esters, hydroxyacrylate esters and partially fluorinated acrylate esters.

Another preferred class of (co)polymers are those obtained by condensation of aldehydes (preferably formaldehyde) and/or ketones such as phenolic resins, particularly neutral phenolic resins, polyaldehyde-keton resins, polyketones, novolaks and resols. Preferably the (co)polymer has an OH value of between 30 and 800 mg KOH g, preferably between 100 and 500 mg KOH/g and a glass transition temperature of between -50 and 150°C, preferably between 0 and 80°C. The molecular weight of the (co)polymer is preferably between 500 and 10000, more preferably between 4000 and 6000. The (co)polymer has preferably a melt range of 60 to 160°C. Optimal results are generally obtained when the aromaticity of the (co)polymer is at least 15 %; the aromaticity being calculated as 7200 x number of aromatic moieties in the polymer / number average molecular weight.

Preferred (co)polymers are copolymers of styrene and hydroxyacrylate and optionally also acrylate. Such copolymers are commercially available, for example, Reactol 180, Reactol 255 and Reactol 100 (all available from Lawter International).

Other preferred (co)polymers which are commercially available from Lawter International are K 1717 (a polyketone), Biresol (a bisphenol A resin), K 2090 (a polyester), K 1717B (an aldehyde-keton resin) and K 1111 (a neutral phenolic resin). The (co)polymers are used preferably in such an amount that the ratio between functional groups in the polyisocyanate (NCO) and in the (co)polymer (OH) is between 8:1 and 100:1, preferably between 2: 1 and 25:1. In absence of the (co)polymers the ratio can be defined as infinite.

In preparing the aerogel/xerogel granules a solution is made of the polyisocyanate, optionally the (co)polymer, and the solvent. Subsequently the catalyst is added hereto.

Alternatively the polyisocyanate and optionally the (co)polymer are dissolved in a marginal part of the solvent; subsequently a solution of the catalyst in the residual amount of solvent is added hereto.

Mixing can be done at room temperature or at somewhat higher temperatures.

In case of low boiling solvents (boiling point below room temperature), for example HCFC

22, the solvent containing the catalyst is added to a pressure vessel containing the polyisocyanate and optionally the (co)polymer under its own vapor pressure.

The solids content of the aerogel/xerogel reaction mixture is preferably between 0.5 and 30

% by weight, more preferably between 1.5 and 20 % by weight, most preferably between 3 and 15 % by weight.

The aerogel/xerogel reaction mixture is left standing for a certain period of time to form a polymeric gel. This time period varies from 10 seconds to several weeks depending on the system and the targeted void size and density. Reaction mixtures containing the

(co)polymer form a sol-gel quicker than those not containing said (co) polymers do. In general gelation is obtained in less than one hour.

Temperatures in the range of from about -50 to about 50°C, preferably from 0 to 45°C may be employed.

In the case of low boiling solvents such as HCFC 22 the pressure in the closed vessel is maintained at its saturated vapor pressure and the gelation reaction is carried out at higher temperatures (preferably in the range 30 to 50°C).

A post cure cycle at elevated temperatures can be included. In case the cure temperature is above the boiling point of the solvent selected the sol-gel must be put in a sealed pressure vessel as is the case when solvents with a boiling point below ambient conditions are used

(for instance HCFC 22).

In order to shorten the total process time microwave or radio frequency waves can be used to heat the sol-gel. Alternatively employing conventional heating to a closed, optionally pressurized, container can accelerate the curing.

Further suitable additives to be used in the aerogel/xerogel preparation process and further suitable processing methods are described in WO 95/03358, WO 96/36654, WO 96/37539, WO 98/44013 and WO 98/44028, all incorporated herein by reference.

After formation of the solid sol-gel and possible cure thereof the solvent needs to be removed.

This can be done via a supercritical drying route as commonly employed for making aerogels or via conventional drying techniques.

The solvent can be removed by, for instance, vacuum drainage and/or vacuum drying.

Alternatively the sol-gel may be heated via radiative heating, convective air heating, radiofrequency heating or microwave heating to evaporate off or to expel the solvent. One preferred way of drying is the combination of vacuum and microwave heating which leads to extremely short drying times.

Another possible process is freeze-drying or a combination of freeze drying with microwave heating.

The aerogel/xerogel granules for use in the presently claimed coating have an average particle diameter of more than 200 μm and preferably less than 2 cm. Preferably the particle size is in the range 0.5 to 15 mm, most preferably in the range 2.8 to 8 mm.

The aerogel/xerogel granules generally have a density of below 350 kg/m , preferably in the range of 60 to 250 kg/m³.

The thermal conductivity at 10°C of the aerogel/xerogel granules themselves (air-filled) is generally lower than 50, even lower than 35 mW/mK. The aerogel/xerogel granules can be added to any one of the reaction components before mixing them or at the mixing.

The aerogel/xerogel granules are generally used in amounts of less than 20 % by weight based on the coating. Preferably the loading of granules is in the range 5 to 20 wt%, most preferably in the range 10 to 18 wt%. The urethane group-containing insulating coating is prepared by reacting an organic polyisocyanate with a polyfunctional isocyanate-reactive compound in the presence of suitable auxiliaries such as blowing agents, catalysts and surfactants.

By the use of appropriate starting materials and suitable amounts of blowing agent, the insulating coatings obtained by the method of the present invention may take the form of rigid foams or microcellular elastomers.

Organic polyisocyanates which may be used in the method of the present invention include aliphatic, cycloaliphatic and araliphatic polyisocyanates, for example, 1 ,6-hexamethylene diisocyanate, 2,2,4-trimethyl-1.6-hexamethylene diisocyanate, isophorone diisocyanate, cyclohexane-l,4-diisocyanate, 4,4'-dicyclohexylmethane diisocyanate and p-xylylene diisocyanate, and those aromatic polyisocyanates conventionally used in the manufacture of polyurethane foams such as tolylene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI) in their various pure, modified and crude forms. Special mention may be made of the so-called MDI variants (diphenylmethane diisocyanates modified by the introduction of urethane, allophanate, urea, biuret, carbodiimide, uretonimine or isocyanurate residues) and the polyisocyanate mixtures known in the art as "crude" or "polymeric" MDI. Isocyanate-terminated prepolymers may also be employed in the present invention. As used herein, the term "isocyanate-terminated prepolymer" is the reaction product of an excess of polyisocyanate and a polyol and includes the prepolymer as well as the pseudo- prepolymer, i.e. a mixture of the prepolymer and the polyisocyanate from which the prepolymer is prepared. The isocyanate-terminated prepolymer useful in the present invention generally has a free isocyanate (NCO) content of from 15 to 32 wt%.

The nature of the isocyanate-reactive compound, which may be used in the present invention, depends on the type of cellular product to be obtained, i.e. rigid foam or microcellular elastomer. For the preparation of rigid foam, suitable isocyanate-reactive compounds will be especially polyols having a molecular weight of 62 to 1500 and a functionality of 2 to 8. especially 3 to 8.

For the preparation of microcellular elastomers mixtures of high and low molecular weight isocyanate-reactive compounds are generally used. Particularly suitable high molecular weight isocyanate-reactive compounds having a molecular weight of 1000 to 10000 and a functionality of 2 to 4 include polyols, polyamines, imine-functional compounds or enamine-containing compounds and mixtures thereof. Especially suitable low molecular weight isocyanate-reactive compounds having a molecular weight below 1000, preferably of 62 to 1000 and a functionality of 2 to 8, may be selected among polyols, polyamines, hydroxy amino compounds, imine-functional and/or enamine-containing compounds or mixtures thereof. Such low molecular weight isocyanate-reactive compounds are used as chain extenders in the preparation of elastomeric foams; a preferred one is butanediol. Polymeric polyols have been fully described in the prior art and include reaction products of alkylene oxides, for example ethylene oxide and/or propylene oxide, with initiators containing a plurality of active hydrogen atoms per molecule. Suitable initiators include water and polyols, for example, glycol, propylene glycol and their oligomers, glycerol, trimethylolpropane, triethanolamine, pentaerythritol, sorbitol and sucrose, and polyamines, for example, ethylene diamine, tolylene diamine, diaminodiphenylmethane and polymethylene polyphenylene polyamines, and aminoalcohols, for example, ethanolamine and diethanolamine, and mixtures of such initiators. Other suitable polymeric polyols include polyesters obtained by the condensation of appropriate proportions of glycols and higher functionality polyols with dicarboxylic acids. Still further suitable polymeric polyols include hydroxyl-terminated polythioethers, polyamides, polyesteramides, polycarbonates, polyacetals, polyolefins and polysiloxanes.

Polyols having a molecular weight below 1000 include simple non-polymeric diols such as ethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol and 1 ,4- butanediol. Polyamines having a molecular weight of at least 1000 include amino-ended polyethers, polyesters, polyesteramides, polycarbonates, polyacetols, polyolefins and polysiloxanes. Polyamines having a molecular weight below 1000 include aliphatic, cycloaliphatic or araliphatic polyamines containing two or more primary and or secondary amino groups, such as the low molecular weight amino-ended polyethers, and aromatic polyamines such as diethyltolylenediamine (DETDA).

Suitable low molecular weight hydroxy-amino compounds comprise monoethanolamine, diethanolamine, isopropanol amine and the like.

Suitable imino- or enamino functional reactants include those compounds which are derived from the modification of the above-described amino-functional compounds, e.g. upon their reaction with an aldehyde or a ketone.

Mixtures of isocyanate-reactive components varying in chemical structure and/or molecular weight and/or functionality may be used, if desired.

Water and or inert low boiling compounds having a boiling point of above -50°C at 1 bar can be used as blowing agent in the presently claimed process. The amount of water used as blowing agent may be selected in known manner to provide foams of the desired density, typical amounts being in the range of from 0.05 to 5 parts by weight per 100 parts by weight of reactive ingredients. For the preparation of elastomeric foams, typical amounts of water will range from 0.05 to 1.5 % by weight of reactive ingredients, preferably not more than 0.5 %, more preferably not more than 0.2 % by weight.

Suitable inert low boiling blowing agents include, for example, perfluorocarbons, hydrofluorocarbons, hydrochlorofluorocarbons, fluorine-containing ethers, fluorine- containing amines, hydrocarbons and dialkylethers.

The total amount of blowing agent used will be sufficient to provide foams of the desired density, suitable amounts for any given density being readily determined by a person skilled in the art. The foam-forming reaction may be advantageously carried out in the presence of one or more catalysts. Suitable catalysts include aliphatic and cycloaliphatic tertiary amines and organometal catalysts such as acetylacetonates and carboxylates based on tin, titanium, zirconium, bismuth, cobalt, nickel, zinc, copper and iron (for example, dibutyltin dilaurate). Preferred catalysts for the preparation of elastomeric foams are organometal catalysts based on bismuth.

In addition to the ingredients already mentioned, the foam-forming reaction mixture may contain one or more other auxiliaries or additives conventional to isocyanate-based foam formulations. Such optional additives include fire retardants, smoke suppressants, organic or inorganic fillers, thixotropic agents, dyes, pigments, mould release agents, surfactants, other chemical blowing agents, foam stabilizers and the like.

Cellular polymeric products may be prepared according to the invention by reacting an organic polyisocyanate with an isocyanate-reactive component at an isocyanate index (ratio of isocyanate groups to isocyanate-reactive groups expressed as a percentage) of between 40 and 300, preferably between 70 and 190, more preferably between 95 and 120, although higher indices, for example up to 1500, may be employed in conjunction with trimerisation catalysts.

The urethane group-containing insulating coatings of the present invention generally have a density of more than 200 kg/m³, and preferably less than 1000 kg/m³. Preferably the density is below 700 kg/m , most preferably below 550 kg/m .

The insulating coatings of the present invention generally have a thermal conductivity at 10°C of less than 120 mW/mK. even less than 100 mW/mK. While the present invention relates to the use of polyisocyanate based aerogel or xerogel granules in urethane group-containing insulating coatings it is clear that these granules can also be used in coatings based on an epoxy or polypropylene or polyethylene matrix. The insulating coating of the present invention can be used in all sorts of applications where coatings are required having a U value of less than 5 W/m K, generally in the range 1.5 to 5 W/m²K.

The insulating coatings can be used for hollow bodies such as drums or pipes, as used in the steel, materials-handling, transport and paper industry. Pipes with an external coating for the industrial, offshore and onshore sectors as well as pipes with an internal coating for the hydraulic conveying of abrasive goods can be produced.

The insulating coating may be applied directly to the surface of the hollow body or to a primed surface such as an anti-corrosion layer or the surface to be coated can be provided beforehand with an adhesion promoter. Preferably the anti-corrosion coating is an epoxy resin. A thermoplastic or thermosetting top coating can be applied to the urethane-based insulating coating. This thermoplastic top coating is preferably selected from the group consisting of polypropylene, polyethylene, polystyrene, polybutene, copolymers based on styrene/acrylonitrile/acrylic ester or acrylonitrile/butadiene/styrene, polyamides, polyesters, polyurethanes and polycarbonates. A thermosetting top coating can, for example, be based on polyurea.

The insulating coating can be provided on the pipes by pouring or applying the material onto a rotating pipe (as described in US 5939145 and US 5601881). Alternatively hollow bodies are manufactured by coating a removable core. In this case, either a release agent is applied to the core or the core must be surrounded with a release foil. Also half shell mouldings can be made.

Typically insulating layers up to about 20-25 mm can be routinely dispensed.

The coating is provided along substantially the whole length of the pipe, ending adjacent the ends of the pipe in order to allow successive pipes to be joined together.

The insulating coating is allowed to cure to a handleable condition. The method of the present invention is suitable for coating or producing bodies having the most varied diameters. In the case of large diameters, use is made of systems, which react more slowly than those for smaller diameters are. For the internal coating of bodies, the exothermic reaction should be adjusted so that excessive contraction stresses do not arise, i.e. products should be used which have been pre-reacted to as high a degree as possible; in other words isocyanate prepolymers should be used.

It is envisaged that the coating described above will be used on pipelines laid to a depth of approximately 1500 m and in temperatures between 0 and 100°C. These figures should not, however, be taken as limits for the use of the coating.

The invention is illustrated, but not limited, by the following examples in which the following ingredients were used:

Polyol 1 : a polyether polyol of functionality 2.59, OH value 35 mg KOH/g and molecular weight 3500.

Polyol 2: a polyol of functionality 2, OH value 1245 mg KOH/g and molecular weight

89.5.

Bicat V: a bismuth containing catalyst available from Shepherd Chemicals, USA.

SUPRASEC 2010: an isocyanate-terminated prepolymer of NCO value 26.2 % available from Huntsman Polyurethanes (SUPRASEC is a trademark of Huntsman ICI Chemicals

LLC).

EXAMPLE

Polyol 1 (99.2 pbw), polyol 2 (24.8 pbw) and Bicat V (0.1 pbw) are weighed off in a 500 ml foam cup. Subsequently the filler (26.55 pbw) is added to this mixture. Then SUPRASEC 2010 (81.4 pbw) is added to the filler/polyol solution and the filler is properly blended in during a short blending time (± 2 minutes). Thereupon the reaction initiates. As filler the following materials were tested:

❖ Scothlite S38 glass microspheres of particle size about 10 μm, density 230 kg/m and thermal conductivity at 10°C 59 mW/mK (available from 3M).

❖ Aerogel granules of particle size more than 200 μm, density 180 kg/m³ and thermal conductivity at 10°C of 20.2 mW/mK (particle size of Aerogel 1 is between 1.4 and 2.8 mm; particle size of Aerogel 2 is between 2.8 and 8.0 mm). These aerogel granules were prepared by the process as described in WO 95/03358 and then reduced in size by means of a mechanical high-speed mixer operated for different time periods to obtain different particle size distributions. The aerogel granules were then passed over mechanical sieves of different mesh to obtain the desired particle size fractions.

Different types of fillers in different amounts were added. The thermal conductivity at

10°C (Lambda) of the final coating was measured according to standard ISO 8301 and also the density according to standard ISO 7345.

The results are presented in Table 1.

These results show that using aerogel/xerogel granules having a particle size of more than

200 μm leads to insulating coatings of lower thermal conductivity and lower density than those of the prior art filled with smaller microspheres.

Table 1

Claims

1. Process for preparing a urethane group-containing insulating coating comprising the step of reacting a polyisocyanate compound with a compound containing at least two isocyanate-reactive hydrogen atoms in the presence of a filler material, characterized in that said filler material comprises polyisocyanate- based aerogel or xerogel granules having a diameter of larger than 200 μm.

2. Process according to claim 1 wherein the aerogel or xerogel granules have a diameter in the range 0.5 to 15 mm.

3. Process according to claim 2 wherein the aerogel or xerogel granules have a diameter in the range 2.8 to 8 mm.

4. Process according to any one of the preceding claims wherein said filler material is used in amounts of less than 20 % by weight based on the coating.

5. Process according to claim 4 wherein said filler material is used in amounts of between 10 to 18 % by weight based on the coating.

6. Process according to any one of the preceding claims wherein said polyisocyanate- based aerogel or xerogel granules are prepared by mixing a polyisocyanate, a catalyst and optionally a polyfunctional isocyanate-reactive compound in a suitable solvent, maintaining said mixture in a quiescent state for a sufficiently long period of time to form a polymeric gel and drying the thus formed gel.

7. Process according to any one of the preceding claims wherein said coating is an elastomeric urethane-based foam.

8. Process according to claim 7 wherein said polyisocyanate is an isocyanate-terminated prepolymer having a free isocyanate content of 15 to 32 wt%.

. Process according to claim 7 or 8 wherein said isocyanate-reactive compound has a functionality of 2 to 4 and a molecular weight of 500 to 10000.

10. Process according to claim 7, 8 or 9 wherein said reaction is carried out in the presence of an isocyanate-reactive chain extender of functionality 2 to 3 and molecular weight

50 to 500.

11. Insulating coating obtainable by the process as defined in any one of the preceding claims.

12. Use of the insulating coating as defined in claim 11 for pipes.