Rigid polyurethane and urethane-modified polyisocyanurate foams are in general prepared by reacting the appropriate polyisocyanate and isocyanate-reactive compound (usually a polyol) in the presence of a blowing agent. Rigid polyurethane foams are well known in the art and have numerous applications, particularly as an insulating material. Examples include insulation of refrigerators and freezers, insulation of pipes and tanks in industrial plants and use as an insulating material in the construction industry.

Large diameter polyurethane pre-insulated pipes are widely used for the transport of oil and chemicals and for district heating and cooling systems.

A number of different production methods can be used for the production of pre-insulated pipes.

In general, one can distinguish between two types of techniques, the discontinuous and continuous production technique. In discontinuous production techniques a pipe pre- assembly is made by positioning the steel inner pipe centrally in a slightly shorter casing pipe.

To keep the steel pipe in the center of the casing pipe, distance holders are arranged around the steel pipe. At both ends the gap between the steel and the casing pipe is sealed off by end- caps that fit tightly around the steel and the HDPE casing pipe. The end-caps are equipped with holes for foam injection and air venting. In principle, pipes of any length up to approximately 16 meters can be used, but standard steel pipe lengths are 6,12 and 16 m.

Continuous pipe production techniques consist of two stages. In a first stage, the foam is applied on the inner pipe. In a second stage, the casing pipe is extruded or wound around the pre-shaped foam. Continuous techniques allow a fast and consistent production of a large number of pipes of the same dimension. Although the initial investment into these techniques may be higher, cost savings are achieved due to reduction of foam filling density and a reduced thickness of the high-density polyethylene (HDPE) casing pipes.

For continuous pipe manufacturing, the continuous spray technique is particularly useful for medium and large diameter pipes. In the continuous spray technique the reacting foam mixture is sprayed on the outside of the rotating medium pipe. Obviously the foam has to react very quickly, so that the foam adheres well to the pipe surface and does not spin of.

Various layers of foam may be applied to obtain the required insulation thickness. Very uniform foam is created over an extremely short flow path. Virtually any insulation thickness can be produced by spray application. Large and long pipes can be insulated using small foaming machines. Afterwards, the HDPE casing pipe is extruded or wound around the insulation. Alternatively, a polyurea coating can also be applied as casing using the spray technique. In comparison to discontinuous pipe insulation, applied foam densities can be lower because of smaller difference between overall and core density. The HDPE casing pipe can be thinner since it does not have to withstand the high foam pressure that occurs during conventional pipe filling and hence, material savings are possible.

Applying the continuous spray technique requires specially formulated polyurethane foam systems. For processing reasons, high foam reactivity is demanded. This increased reactivity is often obtained through high catalyst dosing or through the use of amine initiated polyols that have a high intrinsic reactivity. However, it is well known that the presence of amine groups in the foam network can lead to a reduced thermal stability, in particular the continuous long-term thermal stability might be considerably reduced. It is therefore a challenging target to develop polyurethane systems for this technique that both provide high thermal resistance of the foam and ease of processing.

The combination of good mechanical composite properties and high foam thermal resistance is a particular requirement often encountered in pipe insulation. Obviously, required foam performance properties might vary depending on the end application of the pre-insulated pipes. In district heating applications, a continuous high temperature resistance is demanded for a service period of 30 years. Nowadays, also for oil pipelines that are insulated with polyurethane foam, there is a trend to demand an increased thermal resistance for polyurethane foam.

The present invention aims to provide rigid polyurethane foams having excellent high temperature resistance and excellent mechanical properties, thus making them very suitable as insulating material for steel pipes used in the hot water transportation system of district heating networks and for oil and gas pipelines.

These objects are met by using in the process of making rigid polyurethane or urethane- modified polyisocyanurate foams from polyisocyanates and isocyanate-reactive components

in the presence of blowing agents, a specific isocyanate-reactive composition containing (a) from 20 to 60 wt% of an aromatic polyether polyol, (b) from 20 to 60 wt% of a polyether polyol of functionality 4 or more and (c) from 0 to 40 wt% of a polyether polyol of functionality less than 4, the total amounts of polyols (a), (b) and (c) equal to 100 wt%.

A polyether polyol is obtained by the alkoxylation, i. e. reaction with alkylene oxide, of a suitable polyhydric alcohol initiator. The preparation process is well known in the art.

Alkylen oxides, usually applied, and also useful for the present invention, are ethylene oxide, propylene oxide and butylene oxide, with propylene oxide being preferred for the purpose of this invention.

The aromatic polyether polyol for use in the present invention is a polyether polyol produced from an aromatic amine, a Mannich base having an aromatic ring or a polyfunctional phenol as the starting material. Preferably these aromatic polyether polyols are used in an amount of between 25 and 50 % by weight based on the total of polyols (a), (b) and (c).

The polyether polyol produced by using the aromatic amine as a starting material is a polyol prepared by adding at least one alkylen oxide such as ethylene oxide and/or propylene oxide (preferably solely propylene oxide) to at least one aromatic amine such as the various isomers of tolylenediamine (TDA) (preferably the ortho-and meta-isomers), diphenylmethanediamine (DADPN4) and its higher homologues (polymethylene polyphenylene polyamine), aniline and toluidine. The hydroxyl value of the aromatic amine initiated polyether polyol is usually between 200 and 600 mg KOH/g.

Mannich polyols are a family of polyether polyols constructed from an initiator via Mannich condensation of formaldehyde, alkanolamine and a phenolic molecule. The alkanolamines are usually diethanol and diisopropanol amine. The phenolic species are usually phenol, nonyl-phenol and bisphenol A.

The hydroxyl value of the Mannich base initiated polyether polyols is usually between 170 and 600 mg KOH/g.

Suitable Mannich polyols are described, for example, in US 4137265 and US 4883826.

The polyether polyol of functionality 4 or more is made using an initiator of functionality at least 4 such as sorbitol, sucrose or ethylene diamine. A preferred initiator is sorbitol.

Preferably this high functionality polyether polyol is used in an amount of between 25 and 50 % by weight based on the total of polyols (a), (b) and (c).

The polyether polyol of functionality less than 4 is made using an initiator of functionality

less than 4 such as glycerol and trimethylolpropane. A preferred initiator is glycerol.

Preferably this low functionality polyether polyol is used in an amount of between 2 and 30 % by weight based on the total of polyols (a), (b) and (c).

The hydroxyl value of polyol (a), (b) and (c) generally lies in the range of 200 to 800 mg KOH/g. The total hydroxyl value of the isocyanate-reactive composition is preferably between 400 and 650 mg KOH/g.

At least one of each type of polyol (a), (b) and (c) is used in the process of the present invention. The present invention also covers the use of two or more polyols of type (a), (b) or (c) as long as the total amount of polyols (a), (b) and (c) falls within the above ranges.

Apart from the above specified polyols (a), (b) and (c) the isocyanate-reactive composition may contain other isocyanate-reactive compounds in an amount of up to 10 wt% based on the total isocyanate-reactive composition.

Suitable further isocyanate-reactive compounds to be used in the process of the present invention include any of those known in the art for the preparation of rigid polyurethane or urethane-modified polyisocyanurate foams. Of particular importance for the preparation of rigid foams are polyols and polyol mixtures having average hydroxyl numbers of from 300 to 1000, especially from 300 to 700 mgKOH/g, and hydroxyl functionalities of from 2 to 8, especially from 3 to 8. Suitable 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 from 2 to 8 active hydrogen atoms per molecule. Suitable initiators include: polyols, for example glycerol, trimethylolpropane, triethanolamine, pentaerythritol, sorbitol and sucrose; polyamines, for example ethylene diamine, tolylene diamine (TDA), diaminodiphenylmethane (DADPM) 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 or polycarboxylic acids. Still further suitable polymeric polyols include hydroxyl-terminated polythioethers, polyamides, polyesteramides, polycarbonates, polyacetals, polyolefins and polysiloxanes.

Suitable organic polyisocyanates for use in the process of the present invention include any of those known in the art for the preparation of rigid polyurethane or urethane-modified polyisocyanurate foams, and in particular the aromatic polyisocyanates such as diphenylmethane diisocyanate in the form of its 2,4'-, 2,2'- and 4,4'-isomers and mixtures

thereof, the mixtures of diphenylmethane diisocyanates (MDI) and oligomers thereof known in the art as"crude"or polymeric MDI (polymethylene polyphenylene polyisocyanates) having an isocyanate functionality of greater than 2, toluene diisocyanate in the form of its 2,4- and 2,6-isomers and mixtures thereof, 1,5-naphthalene diisocyanate and 1,4-diisocyanatobenzene. Other organic polyisocyanates which may be mentioned include the aliphatic diisocyanates such as isophorone diisocyanate, 1,6-diisocyanatohexane and 4,4'-diisocyanatodicyclohexylmethane.

A preferred polyisocyanate for use in the present invention is polymeric MDI including the higher functionality variants thereof (functionality of 2.9 or higher).

The quantities of the polyisocyanate compositions and the polyfunctional isocyanate-reactive compositions to be reacted will depend upon the nature of the rigid polyurethane or urethane- modified polyisocyanurate foam to be produced and will be readily determined by those skilled in the art.

Preferably, in order to further increase the long-term thermal foam resistance, the polyisocyanate/polyol volume ratio is higher than 100/100, more preferably higher than 120/100, most preferably around 150/100.

Any of the physical blowing agents known for the production of rigid polyurethane foam can be used in the process of the present invention. Examples of these include dialkyl ethers, cycloalkylene ethers and ketones, fluorinated ethers, chlorofluorocarbons, perfluorinated hydrocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, and hydrocarbons, or mixtures thereof.

Examples of suitable hydrochlorofluorocarbons include 1-chloro-1, 2-difluoroethane, 1- chloro-2,2-difluoroethane, l-chloro-1, 1-difluoroetlaane, 1,1-dichloro-1-fluoroethane and monochlorodifluoromethane.

Examples of suitable hydrofluorocarbons include lower aliphatic or cyclic, linear or branched hydrocarbons such as alkanes, alkenes and cycloalkanes, preferably having from 2 to 8 carbon atoms, which are substituted with at least one, preferably at least three, fluorine atom (s).

Specific examples include 1,1,1,2-tetrafluoroethane (HFC 134a), 1,1,2,2-tetrafluoroethane, trifluoromethane, heptafluoropropane, 1, 1, 1-trifluoroethane, 1,1,2-trifluoroethane, 1,1,1,2,2- pentafluoropropane, 1,1,1,3-tetrafluoropropane, 1,1,1,3,3-pentafluoropropane (HFC 245fa), 1,1,3,3,3-pentafluoropropane, 1, 1, 1,3,3-pentafluoro-n-butane (HFC 365mfc), 1,1,1,4,4,4- hexafluoro-n-butane, 1,1,1,2,3,3,3-heptafluoropropane (HFC 227ea) and mixtures of any of the above.

Suitable hydrocarbon blowing agents include lower aliphatic or cyclic, linear or branched hydrocarbons such as alkanes, alkenes and cycloalkanes, preferably having from 4 to 8 carbon atoms. Specific examples include n-butane, iso-butane, 2,3-dimethylbutane, cyclobutane, n- pentane, iso-pentane, technical grade pentane mixtures, cyclopentane, methylcyclopentane, neopentane, n-hexane, iso-hexane, n-heptane, iso-heptane, cyclohexane, methylcyclohexane, 1-pentene, 2-methylbutene, 3-methylbutene, 1-hexene and any mixture of the above.

Preferred hydrocarbons are n-butane, iso-butane, cyclopentane, n-pentane and isopentane and any mixture thereof, in particular mixtures of n-pentane and isopentane (preferred weight ratio 3: 8), mixtures of cyclopentane and isobutane (preferred weight ratio 8: 3), mixtures of cyclopentane and n-butane and mixtures of cyclopentane and iso-or n-pentane (preferred weight ratio between 6: 4 and 8: 2).

Generally water or other carbon dioxide-evolving compounds are used together with the physical blowing agents. Where water is used as chemical co-blowing agent typical amounts are in the range from 0.2 to 5 %, preferably from 0.5 to 3 % by weight based on the isocyanate-reactive compound.

Water can also be used as the sole blowing agent without any additional physical blowing agent being present.

The total quantity of blowing agent to be used in a reaction system for producing cellular polymeric materials will be readily determined by those skilled in the art, but will typically be from 2 to 25 % by weight based on the total reaction system.

In addition to the polyisocyanate and polyfunctional isocyanate-reactive compositions and the blowing agents, the foam-forming reaction mixture will commonly contain one or more other auxiliaries or additives conventional to formulations for the production of rigid polyurethane and urethane-modified polyisocyanurate foams. Such optional additives include crosslinking agents, for examples low molecular weight polyols such as triethanolamine, urethane catalysts, for example tin compounds such as stannous octoate or dibutyltin dilaurate or tertiary amines such as dimethylcyclohexylamine or triethylene diamine, isocyanurate catalysts, surfactants, fire retardants, for example halogenated alkyl phosphates such as tris chloropropyl phosphate, and fillers such as carbon black.

It is convenient in many applications to provide the components for polyurethane production in pre-blended formulations based on each of the primary polyisocyanate and isocyanate- reactive components. In particular, many reaction systems employ a polyisocyanate-reactive

composition which contains the major additives such as the blowing agent, the catalyst and the surfactant in addition to the polyisocyanate-reactive component or components.

Therefore the present invention also provides a polyisocyanate-reactive composition comprising the present mixture of polyether polyols (a), (b) and (c), optionally together with the blowing agent and/or catalyst and/or surfactant.

The various aspects of this invention are illustrated, but not limited by the following examples.

The following reaction components are referred to in the examples: Polyol 1: A propoxylated glycerol initiated polyol of OH value 240-260 mg KOH/g Polyol 2: A propoxylated sorbitol initiated polyol of OH value 495-525 mg KOH/g Polyol 3: A propoxylated Mannich base polyol of OH value 510-550 mg KOH/g Polyol 4: A propoxylated DADPM base polyol of OH value 485-515 mg KOH/g Polyol 5: A propoxylated glycerol initiated polyol of OH value 635-665 mg KOH/g Surfactant : A silicone surfactant Catalyst: An amine catalyst Isocyanate: Polymeric MDI EXAMPLE 1 The foam ingredients and their amounts are listed in Table 1 below.

Table 1 Blend 1 Blend 2 Blend 3 Blend 4 Blend 5 Polyol I pbw 3. 44 4.04 8.58 24. 29 12. 92 Polyol 2 pbw 44. 65 36.39 34.29 38. 3 25.85 Polyol 3 pbw 32. 63 40.44 42.86 30. 83 Polyol 4 pbw 34. 47 Polyol 5 pbw 8. 62 Glycerol pbw 5. 15 Water pbw 0. 73 0.93 0.64 2.10 0.65 Surfactant pbw 0. 69 0.65 0.69 0.93 0.69 Catalyst pbw 4. 12 4. 21 4.37 3. 55 8.19 HCFC 141b pbw 8. 59 13.34 8.57 8.61 Isocyanate pbw 171 140 140 172 139.94

The foam systems were sprayed using a high pressure Gusmer H-2000-E machine with a GX- 7 spray gun. The equipment allows using a variable mixing ratio of polyol to polyisocyanate.

Polyol and polyisocyanate compositions were pre-heated and the temperature was maintained via temperature controlled hoses. To simulate industrial conditions, the foam was sprayed on an in-house made rotating pipe equipment with outside diameters of 25 and 50 cm.

Foam samples were left to cure for at least 24 hours before cutting and carrying out mechanical tests. The test methods applied are described in the European Standard EN 253, drawn up by the Technical Committee CEN/TC 107 (Draft Revision of EN 253,"Pre- insulated bonded pipe systems for underground hot water networks-pipe assembly of steel service pipes, polyurethane thermal insulation and outer casing of polyethylene", Ed. KL 01, 1997-03-06, (1997), issued by European District Heating Pipe Manufacturers Association, Denmark). Based on tangential shear strength measurements on pipe assemblies that are aged for at least 1000 hours at three elevated temperatures, as a minimum, and assuming an Anhenius-type relationship, the Calculated Continuous Operating Temperature (CCOT) is determined.

The results are presented in Table 2 below for HCFC 141b blown foams and in Table 3 below for fully water blown foams.

By combining the specific polyether polyols (a), (b) and (c) of the present invention, CCOT values exceeding the target of more than 120°C continuous resistance for a period of 30 years were achieved.

The foam softening temperatures (or short-term temperature resistance) were measured on a Perkin Elmer TMA7 Thermal Analysis System in penetration mode using a heating rate of 10°C per minute.

Table 2 Properties Unit Blend 1 Blend 2 Blend 3 Blend 5 Volume ratio polyol/MDI Vol/Vol 100/150 100/125 100/125 100/125 Core Density 9/1 61 40 63 61 Compressive Strength kPa 577 309 573 525 Closed Cell Content % 95 94 94 96 Water absorption after % 3.1 9. 3 3. 3 3.0 boiling test Initial Softening °C 173 141 142 147 Temperature Thermal Conductivity at mW/mK 19.7 18.9 19.2 19.7 10°C CCOT * °C/30 years 140 130 130 130 * calculated Table 3

Properties Unit Blend 4 Volume ratio poIyol/MDIVoI/VoI100/150 CoreDensity g/1 61 CompressiveStrength kPa 509 Closed Cell Content % 94 Water absorption after boiling test % 3.1 Initial Softening Temperature oc 160 CCOT °C/30 years 129 These results show that the selection of polyether polyols of the present invention allows the formulation of foam systems that provide a long-term thermal integrity of the polyurethane pre-insulated pipe composite at continuous service temperatures of ca. 130°C and higher for a period of 30 years. For short-term exposure, the present foam systems can even resist peak temperatures considerably higher than 130°C.